If only he could show us the memo.

"It's still classified, I suppose?" says Secretary of Defense Donald H. Rumsfeld, looking toward his assistant.

"It's still classified," Lawrence DiRita replies, "along with a lot of the underlying planning."

Rumsfeld nods, apparently disappointed. He is interested in sharing the memo because the memo, as he outlines it, demonstrates that his critics are utterly mistaken. He did not dash heedless and underprepared into Iraq. Rumsfeld foresaw the things that could go wrong -- and not just foresaw them, but wrote them up in a classically Rumsfeldian list, one brisk bullet point after another, 29 potential pitfalls in all. Then he distributed the memo at the highest levels, fed it into the super-secret planning process and personally walked the president through the warnings.

"It would have been probably October of '02, and the war was March, I think," of the following year, Rumsfeld explains. "I sat down, and I said, 'What are all the things that one has to anticipate could be a problem?' And circulated it and read it to the president -- sent it to the president. Gave it to the people in the department, and they planned against those things. And all of the likely and unlikely things that one could imagine are listed there. It was just on the off-chance we'd end up having a conflict. We didn't know at that stage."

Some might quibble with Rumsfeld's description of the historical moment. At the time he wrote the memo, dated October 15, 2002, Congress had recently voted to give President Bush complete authority to invade Iraq and topple Saddam Hussein. A White House spokesman had just confirmed that invasion plans were on Bush's desk -- detailed plans, we now know, which Rumsfeld had been shaping and hammering and editing for much of the previous year.

In other words, there was far more than an "off-chance" of conflict. All that remained to be done was for the president to reach his official decision. The train was loaded, its doors were shut, and it was ready to leave the station.

Rumsfeld never pretended there was anything off-chancy about the timing of the memo when he discussed it with Bob Woodward, who wrote about the document in his authoritative history of Iraq war preparations, Plan of Attack. In that account, Rumsfeld portrayed the memo as a warning blast, an attempt to do "everything humanly possible to prepare" Bush for the awful responsibility that had settled onto his presidential shoulders -- and his shoulders alone. For there comes a point when even the secretary of defense must realize that "it's not your decision or even your recommendation," Rumsfeld reflected with Woodward. By which he meant the Iraq war wasn't Don Rumsfeld's decision or recommendation.

As if to underline the point, Rumsfeld also told Woodward that he couldn't recall a moment, in all the months of planning for the war, when Bush asked whether his defense secretary favored the invasion. Nor did Rumsfeld ever volunteer his opinion. ("There's no question in anyone's mind but I agreed with the president's approach," he added.) So what was in the memo? Dire scenarios ranging from disasters that did not happen, such as chemical warfare and house-to-house combat with Saddam's troops in Baghdad, to bad things that have indeed come to pass, such as ethnic strife among Iraq's religious factions and the successful exploitation of the war as a public relations vehicle for the enemies of the United States.

Rumsfeld raises the subject of this memo near the end of an interview in his spacious Pentagon office. Outside the tinted blast-proof windows and across the Potomac, a brutal summer sun bakes the domes and cornices of Washington, but Rumsfeld is wearing a fleece vest over his shirtsleeves. He often finds his office chilly. Rumsfeld appears relaxed, charming, expansive. It seems awfully helpful of him to want to share a classified memo written expressly for the president of the United States, who was wrestling with his awesome power to wage war.

But then you wonder: Why did Rumsfeld write that memo, at that moment, and why is he flagging it now?

If the point of the memo was to nudge George W. Bush's hand from the throttle of the engine, to halt the train of events at the last moment, then it was too little too late. Rumsfeld would have known this after 40 years inside the sanctums of government. Plans have a way of gathering momentum as surely as boulders running downhill. One of "Rumsfeld's Rules," the booklet of maxims and tenets he has coined and updated through his lifetime in management, notes that "it is easier to get into something than to get out of it." The time to stop an idea is before it gets moving.

And if his purpose was to spur adequate thinking and preparation for the complexity of the Iraq mission, he failed. Military experts and strategic thinkers differ over whether the insurgency in Iraq can be quelled and a legitimate government stabilized on a timeline and a budget that the American people will support. Will it turn out to be "the greatest strategic disaster in our history," as retired Army Lt. Gen. William E. Odom, the Army's chief of intelligence and director of the National Security Agency during the Reagan administration, recently asserted? Or will it someday be seen as "a hard struggle" toward an eventual victory, albeit a struggle through "the crucible with the blood and the dust and the gore," as Chairman of the Joint Chiefs of Staff Gen. Richard Myers said in his final congressional testimony in September before retiring? Myers acknowledged that "we've made lots of mistakes along the way." But, he said, that was because "we are trying to do in Iraq what has never been done before."

But there is broad agreement now that if the United States salvages a victory in Iraq, it will come in spite of the initial war planning, not because of it. Rumsfeld's own advisory think tank, the Defense Science Board, took a long look at this issue last year and concluded that the architects of the Iraq war -- led by Rumsfeld -- lacked necessary knowledge of Iraq and its people, and that they failed to factor in well-known lessons of history.

"It is clear that Americans who waged the war and who have attempted to mold the aftermath have had no clear idea of the framework that has molded the personalities and attitudes of Iraqis," the board declared in a report bearing the official seal of the Department of Defense. "It might help if Americans and their leaders were to show less arrogance and more understanding of themselves and their place in history. Perhaps more than any other people, Americans display a consistent amnesia concerning their own past, as well as the history of those around them."

Maybe Rumsfeld's memo was written not just for its moment, but also for the future, as proof that he remained sober even in an atmosphere of neoconservative enthusiasm for the war. Although classified, the memo keeps surfacing in this context, always putting a little distance between Rumsfeld and the audacious gamble in Iraq. Five weeks before the invasion, as others were promising a cakewalk, Rumsfeld and his memo surfaced in the New York Times. It surfaced again with Woodward. And now here it is again.

This subtle distancing explains why the memo has joined other actions and inactions, statements and omissions as evidence, for some of the Iraq war's strongest supporters, that the man atop the Pentagon, despite his bravura, may not have had his whole heart in this war.

The idea may not be immediately obvious to Americans at their dinner tables -- that Donald Rumsfeld, the chesty, confident, competent "Rumstud" of the Iraq invasion briefing room, has held something back from the war effort. He was, after all, the public face of "shock and awe." He seemed to thrive on the glare, the pressure, the workload of war, at his desk daily by 6:30 a.m. and dictating his notorious "snowflake" memos -- the waves of questions and orders and ruminations that swirl through Rumsfeld's Pentagon like a blizzard -- long into the night. He dominated news briefings and congressional hearings like a tank rolling through small-arms fire, and he gloried in the hand-wringing of weaker souls. Behind the scenes, Rumsfeld and his civilian staff bulldozed skeptical generals and smashed rival bureaucracies in the planning and execution of the invasion.

So when William Kristol, editor of the neoconservative magazine the Weekly Standard and a leading proponent of the Iraq war, charged Rumsfeld with insufficient commitment in August, Rumsfeld's assistant fired back with confidence. "Kristol thinks that he senses the 'inescapable whiff of weakness and defeatism' in the leadership of the Pentagon," DiRita wrote. "This is nonsense."

But Kristol remains unpersuaded. "I don't think he ever really had his heart in it," he says. And this is interesting, because one of the main reasons why antiwar critics have included Rumsfeld among the fervent forces behind the war is that he signed a letter in 1998 calling for the ouster of Saddam Hussein -- a letter written by Kristol. "He had nothing to do with making it happen," Kristol says of Rumsfeld. "We just faxed it to him, as one of the usual suspects, and a few days later they faxed back his signature."

The crux of the complaint against the secretary is this: Whenever Rumsfeld has faced a choice between doing more in Iraq or doing less, he has done less. When, during the pre-invasion planning, the State Department sent a team of Iraq experts to the Pentagon to help prepare a major reconstruction effort for the aftermath, Rumsfeld turned some of them away. As a result, "there was simply no plan, other than humanitarian assistance and a few other things like protection of oil and so forth, with regard to postwar Iraq. There was no plan," retired Col. Lawrence Wilkerson, chief of staff to former secretary of state Colin Powell, explained in a recent speech.

When Army generals called for more troops to occupy the soon-to-be-leaderless country, Rumsfeld pushed for fewer. He cut the time for training National Guard units, including the ones that wound up photographing themselves with naked prisoners at Abu Ghraib prison. (He twice offered his resignation when the prison scandal broke. Bush declined.) He blessed plans to begin pulling the invasion force out of Iraq almost as quickly as it went in.

The thread running through all these decisions is Rumsfeld's steady resistance to a long, troop-intensive effort in Iraq. A big part of his job, he explained that day in his office, is to "balance" the resources being poured into Iraq against necessary investments in a transformed, high-tech military force of the future. When senators tell Rumsfeld, as they did again in September, that the United States should have enough troops on the border between Iraq and Syria to cut off the flow of money and manpower to the anti-U.S. insurgency, one can imagine the secretary running through the math. Today's highly skilled volunteer troops don't come as cheaply as the draft-age cannon fodder of wars gone by. With pay, training and benefits, each soldier or Marine sent to secure that border would mean an annual debit of up to $100,000 in defense budgets for years to come. Ten thousand soldiers equals $1 billion. Not counting their guns, ammo, food, uniforms, armor, vehicles.

Which may be why Rumsfeld's military, as of late September, had assigned just 1,000 Marines to cover the western half of the 376-mile border with Syria. Picture five major college marching bands stretched over the distance between Washington and Trenton, N.J.

Doubts about Rumsfeld's priorities have been widespread in Iraq almost from the beginning. Soldiers wondered why they were doing heavy-armor fighting in unarmored trucks. Commanders scratched their heads when Rumsfeld insisted, at a Pentagon news briefing in 2003, that the ongoing war outside their windows wasn't "anything like a guerrilla war or an organized resistance." Kurdish leaders, concerned about a Pentagon cut-and-run, declined to disband their ethnic militias. "They say, 'Put a permanent U.S. base up here and we'll be glad to,'" one Kurdish representative explains.

Such questions took root in Washington a bit later, however. A turning point came in September 2004, with a pair of columns written by the well-sourced conservative Robert Novak. Many pro-war insiders believed that Rumsfeld was the origin of Novak's startling declaration that "inside the Bush administration policymaking apparatus, there is a strong feeling that U.S. troops must leave Iraq next year. This determination is not predicated on success in implanting Iraqi democracy and internal stability. Rather, the officials are saying, Ready or not, here we go." Bush quickly shot down the trial balloon, but Novak stood fast, pointedly boasting in a follow-up piece that Rumsfeld had not repudiated the original column.

West Point military historian Frederick Kagan soon published a scathing assessment of Rumsfeld's war leadership. A supporter of the decision to invade Iraq, Kagan was appalled that Rumsfeld had not shifted his fabled intensity from visions of future warfare to the burgeoning war of today. "The secretary of defense simply chose to prioritize preparing America's military for future conventional conflict rather than for the current mission," Kagan wrote in Kristol's magazine. "In no previous American war has the chief of the military administration refused to focus on the war at hand." Defenders rose to Rumsfeld's side. The venerable conservative magazine National Review, while critical of Rumsfeld for underestimating the "magnitude of the task that rebuilding and occupying Iraq would present," opened its pages to rebuttals of Kristol's neocon journal. Victor Davis Hanson of the Hoover Institution chalked up America's troubles in Iraq to the huge cuts in active-duty troops that were begun by the first President Bush and continued under President Clinton. "In reality, [Rumsfeld] has carefully allotted troops in Iraq because he has few to spare elsewhere -- and all for reasons beyond his control," Hanson argued.

Others praised Rumsfeld's creativity in squeezing the most from existing troop levels by moving uniformed soldiers and officers out of jobs that civilians could fill instead. Some writers and politicians who could find little to praise in Rumsfeld's handling of post-invasion Iraq nevertheless hailed his willingness to cut outmoded weapons programs and shift forces away from Cold War bases.

"Mr. Rumsfeld, standing on his remarkable record of achievement, is far too effective a defense secretary for any serious student of recent American history to think that he should be replaced," former House speaker Newt Gingrich summed up in the Baltimore Sun.

The man himself seems impervious to these storms. As Rumsfeld reflected on his eventful tenure from an armchair near his big desk last summer, the most striking thing about him was how upbeat he appeared to be. Public support for the Iraq war was plunging. Criticism of him was spreading among the military brass and through Congress. Learned essays were circulating through war colleges and think tanks describing an Army near the breaking point under the pressure of the war -- equipment wearing out 15 times faster than anticipated, the divorce rate among officers tripled. Yet Rumsfeld radiated good cheer as he described his invigorating tussles with a Pentagon bureaucracy that is, by his reckoning, not much advanced beyond inkwells and steam.

His staff reflects that sunny superiority. "The ramparts of Washington are littered with the bleached bones of people who said Donald Rumsfeld was not going to survive," DiRita says happily. Rumsfeld's serenity comes from a distinctive blend of freshness and age. DiRita describes his boss as thirsty for new knowledge and also supremely confident in himself, able to make tough decisions without fretting or second-guessing. "He is always looking forward. He has a sense of himself, and the president likes that," the assistant says. "When you know who you are, you're pretty comfortable with the scrutiny that comes from public service."

At 73, Rumsfeld is the oldest person ever to run the Pentagon, having also been the youngest when he was appointed for his first tour in 1975. Yet, apart from a slight hearing loss that can seem to wax or wane depending on whether he likes what he is hearing, he bears little sign of age. His back is straight, eyes are clear, body is lean, mind is sharp, and he enjoys whipping much younger men in his afternoon squash matches. Only two secretaries of defense have served longer -- Robert McNamara in the 1960s and Casper Weinberger in the 1980s -- and Rumsfeld shows no sign of flagging.

If only he could have had the war he wanted, instead of the war he got. Rumsfeld hoped and intended that Iraq would be a proving ground for his theories about a new era of warfare -- fast, light, "agile," high-tech and overwhelming. Instead, Iraq is an old-fashioned war, hot and dusty, of foot soldiers, fortified camps, checkpoints and armor. Rumsfeld stubbornly clung to his hope even after most others had faced reality. The CIA concluded by June 2003, two months after the liberation of Baghdad, that the United States was facing a "classic insurgency," but Rumsfeld specifically denied it until he was publicly corrected by his able commander, Army Lt. Gen. John P. Abizaid.

Perhaps this is understandable, because the implications of the insurgency -- namely, a long, expensive military and political commitment -- were potentially ruinous for Rumsfeld's larger, futuristic agenda. But the reluctance of the man at the top of the Pentagon to come to grips with the reality on the ground had an impact, according to retired Army Gen. Barry McCaffrey, who surveyed Iraq last summer and reported on his findings to the Senate Foreign Relations Committee.

McCaffrey did not mention the secretary of defense by name in his report. But his terse, grim recounting of America's first 22 months in Iraq led directly to Rumsfeld's door.

"The enterprise was badly launched," McCaffrey wrote. The U.S. invasion "left a nation without an operational State." Rumsfeld's "overwhelmed, under-resourced" appointees were feckless in filling that void. Mistakes were made with alacrity, but effective corrections seemed to take forever. A year passed before the United States began serious and effective training of new security forces for Iraq -- indeed, the United States transferred sovereignty to a provisional Iraqi government in June 2004 without any competent Iraqi military or police units to defend that government. In the meantime, Iraq devolved into "a weak state of warring factions."

No student of history should have been surprised by the insurgency. For centuries, guerrilla tactics have been the preferred strategy of the outgunned and outsoldiered, because insurgency offers a way of winning a war without having to conquer a superior army. Like mosquitoes ruining a picnic, insurgents patiently sap the superior army's will to hold a city, province or country. Kalev Sepp, a retired Special Operations officer and adviser to U.S. commanders in Iraq, published an influential essay last spring in Military Review, an official Army publication, in which he identified more than 50 insurgencies around the world during the past century, ranging from the second Boer War in South Africa to the Hukbalahap Rebellion in the Philippines to the ongoing Russian campaign in Chechnya. Other writers have traced the history of insurgency to the Roman Empire.

After much wheel-spinning, lessons drawn from those examples are finally shaping the U.S. approach in Iraq. "We've crafted a strategy for success in Iraq based on historical lessons [and] counterinsurgency principles," Iraq commander Gen. George Casey recently testified before Congress. This strategy, Casey said, calls for an effort more political than military, precisely the sort of "nation-building" once scorned by Rumsfeld and Bush. The goal is to "enable the Iraqis to take charge of their future." Ordinary Iraqis won't fully turn against the insurgents until they can rely on a competent government to meet basic human needs -- for safety, economic opportunity, reliable infrastructure and so on.

Counterinsurgency is a matter of turning on the air conditioning and keeping it on. Of guaranteeing Iraqis that they can take a government job without fear that their children will be kidnapped as punishment. It is a question not just of sweeping the insurgents from Samarra or Fallujah or Ramadi, but of keeping such cities safe for the long run. The average counterinsurgency effort lasts nine years, Casey informed Congress, "and there's no reason that we should believe that the insurgency in Iraq will take any less time to deal with."

McCaffrey concluded after his visit that the U.S. Army and Marine Corps have indeed landed on the right strategy and are finally making progress. Credit, he said, belongs to the "superb" senior generals who took over after the chaotic first months, and to the soldiers and Marines comprising "the most competent and battle-wise force in our nation's history." His silence concerning civilian leadership of the Pentagon spoke volumes.

Rumsfeld's support continues to dwindle. He has alienated a fair percentage of America's officer corps, though few of them will say so on the record. The boss pays meticulous attention to the selection and promotion of new generals, "constantly scanning the bench: who's coming up," says his assistant, DiRita. Focusing on personnel is a way of putting his lasting stamp on military culture, Rumsfeld believes. It also has the effect of reminding officers that he is watching them carefully.

Nevertheless, the brass has ways of making itself heard. Opinions are expressed to trusted friends, retired comrades, veteran reporters. The tone of that feedback has become so negative that even some pro-Rumsfeld analysts now doubt his effectiveness. Jack Kelly, a former Marine and Reagan-era Pentagon official, is a good example: In his Pittsburgh Post-Gazette column, Kelly recently called for Rumsfeld to resign, even though in many ways he "has been a terrific secretary of defense . . . Army officers think Rumsfeld has it in for them," Kelly wrote. "I don't think that is true. But when a perception is as widespread as this one is, it becomes a reality."

Another well-connected conservative, Loren Thompson of the Lexington Institute, once regarded Rumsfeld as "the most persuasive proponent of the Bush Administration's muscular approach to global security." Now: "From the disarray of 9/11 to the decay of the Western alliance to the debacle of the Iraq occupation to the disorg-anized oversight of Pentagon procurement, Rumsfeld has served the president badly."

Then there's Congress. The secretary has always had a prickly relationship with Congress, which he and most defense analysts regard as too protective of obsolete military bases and big-ticket weapons. When Rumsfeld returned to the Pentagon in 2001 after 24 years away, he was shocked to see the extent of congressional nitpicking and micromanaging. "The number of congressional staffers [devoted to Pentagon issues] had doubled from something like 8,000 to . . . something like 16,000," he marveled. Those staffers demand hundreds of annual reports on a stupefying array of topics, he complained, many of marginal value. "There's so many hands on the steering wheel."

Rumsfeld did a bad job of masking his feelings. As his friend of more than 40 years, Nixon-era defense secretary Melvin Laird, complained recently in Foreign Affairs magazine, Rumsfeld's "overconfident and self-assured style on every issue . . . did not play well with Congress." He warned that this "sour relationship on Capitol Hill could doom the whole [Iraq] effort."

Lately, though, the Republican-controlled Congress has gone past pestering to near repudiation of the secretary. Sen. John Warner (R-Va.), chairman of the Armed Services Committee, recently returned from Iraq dismayed by the sorry state of the country's infrastructure, 2 1/2 years and an ocean of money after the U.S. arrival. He concluded that "the secretary of defense . . . was not, in my judgment, showing the strength and decisiveness that is needed at this time."

As a further rebuke, Warner joined most of the Senate Republicans and all of the Democrats in approving an amendment, 90-to-9, that would require clear rules for the treatment of enemy prisoners under Rumsfeld's jurisdiction.

This scolding of the administration was sponsored by Sen. John McCain (R-Ariz.) -- which only underlined how irritated many senators have become. A high-profile bill that might advance the fortunes of McCain? There are few things conservative Republicans dislike more.

Rumsfeld, apparently, is one.

Why Rumsfeld, one of the smartest, most energetic and most forceful men to serve as secretary of defense, has reached this point is one of the deep riddles of today's Washington. The search for an explanation unfolds through scores of essays and articles, thousands of pages of briefing transcripts and congressional testimony, reams of Pentagon documents and hours of interviews with Rumsfeld watchers inside and outside the military. Few of these interviews could be conducted on the record, because Rumsfeld continues to exert significant control over promotions of those in uniform, and wields influence over Department of Defense contracts with the institutions that employ many outside experts.

Moreover, the war in Iraq has been intensely politicized, to the point that a number of people who agreed to discuss Rumsfeld would not speak on the record because they worried that their assessments would be attacked as politically motivated.

This inquiry also included, at an early stage, an interview with Rumsfeld, in which he was asked to sum up, in general terms, his broad agenda of the past five years. At the end of that conversation, he smiled and said, "Ask me something harder." But repeated requests for a second meeting to pose specific follow-up questions were unavailing. An e-mail containing specific questions was sent to DiRita last month, but neither he nor Rumsfeld responded.

So, return to the beginning: Iraq was not Rumsfeld's decision, nor did he ever formally recommend the invasion. It is not "Rumsfeld's war." His assistant is emphatic on this point. "No. It is America's war," DiRita says.

When Bush drew a bead on Iraq late in 2001, as U.S. forces and allies were taking control of Afghanistan, Rumsfeld was already deeply involved in two wars much closer to home. One was his campaign to remake the Pentagon for the 21st century. The other was a bureaucratic battle with then-Secretary of State Powell. It is impossible to understand Rumsfeld's approach to Iraq outside the context of these earlier, ongoing fights.

First, the war with Colin Powell.

The bitter lawsuits over the 2000 presidential election left Bush under enormous pressure as he chose his first Cabinet. Time was short and the country divided. Bush turned to Powell, a figure so broadly popular that he had been approached about running for vice president by both the Republicans and the Democrats. Powell had foreign policy acumen, military experience and the assurance that comes from years in command -- all areas in which Bush could use a boost.

Still, Powell's prominence and his

politics "raised anxieties" among some important members of the president's inner circle, as journalist James Mann explained in Rise of the Vulcans, his intellectual history of the Bush national security team. The general angered conservatives by favoring affirmative action and abortion rights. And he worried hawks with his Powell Doctrine for war-fighting -- it was much too cautious, they felt.

One of those conservative hawks was Vice President Cheney, whose differences with Powell went back a decade to the first Gulf War. Then, Powell was chairman of the Joint Chiefs of Staff, and Cheney was secretary of defense. Powell tried an end run around Cheney to appeal directly to President George H.W. Bush not to wage war against Iraq. When Cheney discovered Powell's maneuver, he ordered the general to "stick to military matters." Still, Powell succeeded in shaping the Gulf War

strategy according to his principles of decisive force and a clear postwar exit strategy.

This political and personal baggage carried into the new Bush administration. "The overriding dynamic of the Bush foreign policy team," Mann wrote, was an "intense, continuing desire . . . to limit the power and influence of Colin Powell." Job One was to cut off Powell's sway at the Pentagon, an institution he knew as intimately as anyone in government. Cheney and Bush turned to Rumsfeld, Cheney's longtime mentor and pal. Their partnership went back to the Nixon administration, when a young Don Rumsfeld gave an even younger Dick Cheney his first job in the executive branch.

Few men of the past half-century were better suited to intramural bureaucratic combat than Rumsfeld. As a Princeton wrestling champion in the 1950s, his specialty was taking down opponents, an art rooted in quickness, leverage and a ruthless eye for vulnerabilities. He translated these skills to politics and quickly made his reputation on them.

The story has been told many times. How in 1962, after a stint as a Navy fighter pilot, Rumsfeld was elected to Congress at age 30 from suburban Chicago and almost immediately helped organize a coup to oust the veteran House Republican leader, replacing him with genial Gerald R. Ford of Michigan.

How Richard M. Nixon noticed the tough young man and recruited him to run an anti-poverty program. How from that unlikely post, Rumsfeld picked a fight with Nixon's foreign policy guru, Henry A. Kissinger, arguing that Kissinger was too slow to pull out of Vietnam. How Ford found himself president after Nixon's disgrace and called Rumsfeld before he called anyone else. How Rumsfeld, as Ford's chief of staff, pulled off a "Halloween massacre" that finally reduced Kissinger's power over foreign policy, while installing Rumsfeld as the nation's youngest-ever secretary of defense (and moved Cheney up a step, too, making him the youngest White House chief of staff).

How Rumsfeld also orchestrated the dumping of Kissinger's original patron, Nelson A. Rockefeller, as Ford's 1976 running mate.

Fred Ikle, a pillar of the conservative defense establishment, paused a moment when asked to sum up Rumsfeld's style. "Let me put it this way," he said at last, "I would not like to be on the opposite side of an interagency clash from him."

Rumsfeld clashed with Powell almost immediately after Bush was inaugurated in 2001. The issue was China. Powell was quoted characterizing the United States and China as friends, even as Rumsfeld was framing his first major strategic document, the 2001 Quadrennial Defense Review, around the idea of China as a rising threat. Asked about the dispute at the time, Rumsfeld made a joke at Powell's expense. They agreed on "everything," Rumsfeld said, "except those few cases where Colin is still learning."

The laughter stopped as the Iraq invasion approached. According to Wilkerson, Powell's chief of staff at the State Department, a "cabal" of Rumsfeld and Cheney "flummoxed the process" of planning the war. They carried their ideas in "secret" directly to Bush for decisions; meanwhile Rumsfeld authorized his staff to "tell the State Department to go screw itself in a closet somewhere."

Anything Powell favored, the Defense Department opposed. Powell suggested more allies; Rumsfeld announced he was ready to go it alone. Powell favored a larger force; Rumsfeld weeded out troops unit by unit. Ultimately, the invasion was a repudiation of the Powell Doctrine in U.S. military affairs. The force deployed was light and lethal -- but not, history has clearly shown, the master of all contingencies. Nor was there a clear exit strategy, merely the hope of garlands and easy reconstruction -- a point war critics have often made and Rumsfeld has never rebutted in detail.

As for Rumsfeld's war on the military culture, Bush fired the first shot in January 2001. Standing alongside his new defense secretary, Bush promised that Rumsfeld would "challenge the status quo inside the Pentagon." This formulation appealed to Rumsfeld, who had spent the quarter-century since his first Pentagon tour in private business, making a fortune by shaking up under-performing companies.

Diving in, he found his marching orders in a speech given by candidate Bush at the Citadel in 1999, calling for a "transformation" of the great but lumbering U.S. military. The Cold War force was built around big foreign bases and heavy weapons "platforms," such as tank columns and aircraft carriers. With the Cold War over, Bush said, America should use the chance to "skip a generation" of weaponry and tactics to seize the future of warfare ahead of everyone else. A transformed military would be lightly armored, rapidly deployable, invisible to radar, guided by satellites. It would fight with Special Operations troops and futuristic "systems" of weaponry, robots alongside soldiers, all linked by computers. This force would be unmatchable in combat, Bush predicted, but it should not be used for the sort of "nation-building" that characterized Pentagon deployments to Haiti and the Balkans under Clinton.

Little of this was entirely new. Since Vietnam, Pentagon leaders -- including the younger Rumsfeld -- had been searching for more efficient, less entangling, ways to project U.S. power. Even the Army, perhaps the most hidebound of the services, had begun a complete reorganization to make itself easier to deploy. "Some things had been done since the end of the Cold War," Rumsfeld conceded in the interview.

But the Pentagon is the world's biggest, richest bureaucracy, with an annual budget larger than the entire economies of all but about a dozen nations -- bigger than Switzerland or Sweden. The leviathan managed to shrug off most deep and lasting changes. Thus, when Rumsfeld took office in 2001, he recalled, "we were located pretty much where we had been located, geographically, around the world. We still had the same processes and systems and approaches."

Some of the most important changes on Rumsfeld's menu were also the toughest, because of the entrenched interests involved. Weapons programs and bases provide jobs in nearly every congressional district. Republican or Democrat doesn't matter when it comes time to protect those jobs, so the programs and the bases endure even after the strategy behind them has expired. Some defense secretaries quail before this status quo, but not Rumsfeld. Shortly after taking office, he began questioning continued funding for the Crusader supercannon, an artillery piece designed to destroy Soviet tank columns that no longer existed, and the Comanche helicopter, another Cold War relic. Such efforts made him a hero in the military think tanks but earned him a lot of enemies on the Hill. By late summer 2001, Washington was buzzing with rumors that Rumsfeld would soon resign.

Then came September 11.

Rumsfeld dazzled the public and his troops with his cool courage on that fateful morning. When American Airlines Flight 77 plowed into the Pentagon, he rushed to the sound and shudder of the blast and began rescuing victims. Cheney later told a friend that this moment completely remade Rumsfeld in the eyes of the military, and Rumsfeld seized this second chance.

"The war comes along," Rumsfeld recalled, "and a lot of people said you can't do both -- there's no way you can continue to transform that department and . . . deal with the war simultaneously . . . [But] the war gives an impetus to it, a sense of urgency. One of the things that big institutions need is a sense of urgency. They are so lethargic . . . Well, the war created such a sense of urgency that those things are getting fixed. And they're getting fixed . . . a whale of a lot faster than might otherwise be the case because there's a penalty for not fixing them fast."

Buoyed by early successes of Special Ops forces and satellite-guided bombs in Afghanistan, Rumsfeld turned the run-up to Iraq into a transformation workshop. The Pentagon already had a plan for the possible toppling of Saddam Hussein; it was now taken from the shelf and completely remade under Rumsfeld's steady pressure. Generals and civilians involved in the process endured Rumsfeld's favorite management technique -- a brand of relentless interrogation known as "wirebrushing." Many grew frustrated at the fact that Rumsfeld always had a million questions -- but rarely said openly what he wanted or believed.

Editing and badgering, Rumsfeld cut the troop strength in the invasion plan by more than half, and cut the deployment time by months. Instead of a bombing phase led by the Air Force and Navy, followed by a ground war phase of soldiers and Marines, the secretary pushed for a truly joint operation, all branches of the military working together on a blitz to Baghdad. The dream of America's defense secretaries for a half-century -- genuine cooperation among the military services -- came to life.

Combining the audacity of Grant at Vicksburg with a degree of speed and precision never before seen on Earth, the invasion of Iraq "was the utter vindication of Rumsfeld's transformation," an impressed European diplomat said not long ago. "And," he added, "also its downfall." For there was a crack in this machinery that would be exposed if Iraq was not wrapped up quickly.

Rumsfeld spoke of this internal flaw, briefly and elliptically, during the interview in his office. He was describing the Pentagon as an Industrial Age contraption of rattling "conveyor belts" onto which huge weapons purchases and fat plans are loaded months and even years before they will come to fruition. The belts clatter along, beyond human reach, until finally they dump their loads, whether or not America needs them anymore.

"To have affected it, you had to have affected it five or six years ago -- or at least two or three years ago," Rumsfeld said of the system. So his mission, as he described it, was to get his hands into the machinery and start hauling resources off some belts so he could load new projects onto others. "I've had to reach in and grab all those conveyor belts and try to make them rationalize, one against another." This process of moving resources from belt to belt he calls "balancing risks." As in, the risk of not having a supercannon, compared with the risk of not spending enough money on satellites.

This is where the problem of Iraq came in. Rumsfeld explained that he has had to "balance risks between a war plan -- an investment in something immediately -- and an investment in something in the future." This opened a small window into a very important section of his thinking. Bush recently compared the war in Iraq to World War II, which implies a total commitment. Without a doubt, from Pearl Harbor to V-J Day, the war effort was the only military conveyor belt worth mentioning. By contrast, Rumsfeld has conceived of Iraq on a smaller scale, as just one of many hungry conveyor belts inside his Pentagon.

He understood that as soon as the Iraq belt started rolling, it would carry resources away from his preferred investments in the future. So he speaks of his job as a matter of reaching onto that belt and pulling stuff off. "Balance" in this context is another word for "limit" -- limit the amount of money, troops, staff and materiel bound for Iraq. The war he wanted was a short one, involving a relatively small force that would start heading home as soon as Saddam was chased from his palaces. When Army generals urged him instead to load the Iraq conveyor belt with enough troops to fully occupy the country -- securing captured weapons depots, patrolling borders, ensuring order -- Rumsfeld saw the large fixed cost involved in recruiting and training thousands of new troops, a cost that would rattle down Pentagon belts for years to come. He tried to balance those risks of chaos against the conveyor belts that could otherwise be loaded with resources destined for future transformation.

It was a gamble, and one he has stuck with through round after round of raised stakes. Of course, the irony is that the Iraq effort has been the opposite of cheap and short. Despite Rumsfeld's best efforts, it is a budget-buster, and one can almost hear the conveyor belts destined for his transformed tomorrow grinding to a halt, one by one.

It is easier to get into something than to get out of it . . .

Another of Rumsfeld's Rules is the reminder that staff members, no matter how senior, are not the president of the United States. This, too, is central to an understanding of Rumsfeld's relationship to the war in Iraq. He didn't tell the president what to do because that wasn't his job. Some decisions, such as the decision to go to war based on a certain set of assumptions and a particular set of plans, belong to the president alone. "George Bush deserves the credit or blame for the war," says Michael O'Hanlon, a defense analyst at the Brookings Institution. "Rumsfeld gets the credit or blame for the execution."

The next few months could shed a lot of light on the ratio of credit and blame. Progress toward victory would make the earlier mistakes seem smaller. Gen. Casey told Congress in September that the United States has entered a critical period for its counterinsurgency strategy. The tenuous political structure of Iraq will either begin to solidify around the new constitution and next month's parliamentary elections, or it will fall apart. Civil war could doom the attempt to raise and train an Iraqi army that represents all factions of the country. But if, step by step, ordinary Iraqis decide to reject the insurgency and drive out foreign jihadists, then violence should ebb. American public support for the war might rebound. Iraqi troops could take the place of Americans, and U.S. ground troops could start to come home.

That's the hope.

"But if this becomes the next Lebanon," O'Hanlon adds, with the United States withdrawing in haste, and a shattered country left behind, then Rumsfeld's "reputation will go down among the worst secretaries ever."

And what about Rumsfeld's other wars? The first was a rout. Colin Powell has returned to private life, having been dropped, flipped and pinned in short order by the king of the bureaucratic wrestlers. It wasn't really a fair fight -- there was a tinge of World Wrestling Federation tag-teaming when Cheney joined Rumsfeld in pummeling Powell. But the former secretary of state is too much a loyal soldier to talk about it even now, Wilkerson, his former aide, explained.

The verdict on Pentagon transformation may come in February, when Rumsfeld will become the first secretary of defense to publish two Quadrennial Defense Reviews. Congress has mandated these head-to-toe examinations of U.S. defense needs every four years since the early 1990s. Rumsfeld's first QDR was virtually finished on September 11, 2001, and so it barely reflected, in a hastily drafted introduction, the new war on terror.

The new document will show how the hard reality of Iraq has altered Rumsfeld's original futuristic, China-focused vision. Acting Deputy Secretary of Defense Gordon England is in charge of preparing the QDR, and in a recent interview he sketched a picture different from Rumsfeld's original signature ideas. Robots, computers, missile shields and orbiting lasers address threats that no longer seem as pressing. The someday menace of enemy missiles has faded compared with today's car bombs, suicide vests and that medieval remnant, beheadings.

This time around, England said, attention will be given to various back-office reorganizations that will surely glaze the eyes of those who once thrilled to Rumstud. "The business practices, and acquisition process, and the personnel systems for human capital management," England listed. "That's of great interest to Secretary Rumsfeld and to me." Even among Demo-cratic defense experts, Rumsfeld gets a lot of credit for tackling these dull-but-important issues. Still, speeding up the hiring of Arabic speakers, or streamlining the process for acquiring the next-generation of bomb detectors -- while of great value -- is a far cry from changing the very nature of war.

In that sense, perhaps the greatest transformation at the Pentagon during Rumsfeld's tenure will turn out to be the transformation of Donald Rumsfeld.

Even so, Iraq still won't loom largest on Rumsfeld's horizon. As England, his deputy, put it: Iraq "is just a small part of a long war in many places."

So finish there, with the "long war in many places"? How is that going?

Gen. Abizaid, the senior officer in the Central Command -- which covers Iraq, Afghanistan and many other hot spots -- appeared before the Senate Armed Services Committee not long ago. He said he saw progress in Iraq, but mostly wanted to talk about the "al Qaeda threat as the main threat that we face."

"Its global reach and its ability to inflict damage should not be underestimated," Abizaid said. "This enemy seeks to acquire weapons of mass destruction and will certainly use such weapons if they obtain them . . . They experimented with anthrax in Afghanistan. They tried to develop crude chemical weapons in Afghanistan. They are always talking about how they might develop a radiological dispersal device. If they could buy or acquire a nuclear weapon, they would. This is not my guess, this is what they say. It's well known they want to do this, and they'll stop at nothing."

Abizaid continued through a catalogue of fears both urgent and numbingly familiar. Neither journalists nor senators seemed to be paying rapt attention, and so there was little comment when the general reached his conclusion. Which was:

A full four years after the destruction of the World Trade Center and the bombing of the Pentagon, America's national security apparatus is still not properly arranged for the fight against terrorism. "We are not yet organized to the extent that we need to be to fight this enemy," Abizaid said. "We have time to do that, but we need to seize the moment."

Rumsfeld, seated with Abizaid at the witness table, might find in those words a mission worthy of his energy and passion. Iraq may have cost him his chance to remake the wars of the future. But there is still the unfinished job of getting ready for the war we're in right now.

David Von Drehle is a staff writer on the Magazine. He will be fielding questions and comments about this article Monday at 1 p.m. at washingtonpost.com/liveonline.