Every few days, Sen. Edward M. Kennedy can be seen on Capitol Hill hitting tennis balls to his Portuguese water dogs, Sunny and Splash. He typically does this on a grassy area near his office in the Russell Building or, if he has time before work, on a field near the entrance to the FDR Memorial.

"Now whaddaya want, now whaddaya want?" the senator yells to Splash, playfully whacking him on the head. "Good boy, yes, yes -- g'boy, g'boy." Kennedy shouts -- if one can imagine this -- in an upper-crust New England dialect of canine baby talk. "Gimme the booolll now, gimme the booolll now."

Tourists stop, do a double take. Kennedy is the rare figure who is so entrenched in the nation's political scenery that it feels slightly surreal to see him in the flesh.

Is that Ted Kennedy? Or some guy wearing a Kennedy mask?

The image of Kennedy in person is even more startling when his white dress shirt is soaked with sweat and he is carrying a bag of dog poop. That was the case on a recent Friday morning as Kennedy hauled himself around the grass near the FDR Memorial. "You've gotta like a senator who is a pooper picker-upper," says one onlooker, Connie Thompson of Laurel.

Jim Manley, Kennedy's press secretary, offers to take the bag. But the senator waves him away with his tennis racket. There is principle at stake here, which is more important than a poopless photo op: Kennedy is a figure of larger-than-life personality, achievement and baggage who remains at ease with dirty work, be it in the service of his dogs or a presidential campaign.

He looks all of his 72 years -- jarringly so, given that the country met him as a young man and little brother. He wears his mileage plainly: His purply-red cheeks have gone puffy, his hair a bright white. He suffers chronic back pain, hunches and grimaces while he walks, and his breathing is labored after just minimal exertion. "Okay, I think they've had enough," Kennedy says of the dogs, who are yapping and darting around in a tizzy, seemingly eager for more boooll.

Kennedy is enduring a procession of dog days, packed with hearings, votes and debates. Later, he will fly to the family compound in Hyannis Port, Mass., where he will talk frequently by phone with Mary Beth Cahill, John Kerry's campaign manager and Kennedy's former chief of staff.

Kennedy says he hasn't been as active in a presidential race since he himself sought the office in 1980. He calls this "the most important election of my lifetime," and although this has become a hackneyed phrase, it is still revealing, given that Kennedy and two of his late brothers have all run for president themselves.

"This is like oxygen for him," Rep. Patrick Kennedy (D-R.I.) says of his father's role in the Kerry campaign. Ted Kennedy's involvement is even more notable this time since, until recently, he and Kerry had a mutually wary relationship.

But Kennedy is reveling in his understudy's role in this election to a degree that has stunned many Kennedy watchers, including Kerry."It's been unbelievable to me, above and beyond what I would have ever expected," Kerry says. "He's given me advice, he's surrogated for me, he's been out with my family. He's done a million things I could never even recount."

Kennedy has spent hours on the phone in recent weeks talking to negotiators in a labor dispute between Boston officials and the police union that could threaten the Democratic convention in his home town later this month. He worked to obtain $25 million in federal money for security costs at the convention. He has -- according to one campaign aide -- become a kind of X-factor in Kerry's inner circle, someone whose advice Kerry will often seek out and whose counsel often never goes beyond the two of them.

Kerry calls Kennedy "one of the smartest strategists I've ever been around, and one of the smartest hands there is at actually getting things done." Kerry says it would be "impossible to quantify" how often he speaks to Kennedy. Kennedy says he tries to go through Cahill and "stay out of John's way."

Kennedy attributes his involvement in the Kerry campaign to a "confluence of factors," one of which he says is a genuine affection for Kerry and another of which is his disaffection with George W. Bush. Friends say Kennedy feels betrayed by Bush, with whom he collaborated on two of the administration's signature domestic accomplishments -- the education and Medicare bills.

Several leading Democrats are saying that Kennedy's prime-time speech July 27, the convention's second night -- whether combative or statesmanlike -- could set the tone for the rest of the week and perhaps for the fall campaign.

There will be a "Tribute to Ted" concert at Symphony Hall, featuring the Boston Pops and U2's Bono, and cellist Yo-Yo Ma. He will host the dedication of a public green to honor his late mother, Rose Kennedy, and a star-packed fundraiser for the Robert F. Kennedy Memorial. One hundred hotel rooms have been reserved for members of the Kennedy family and his extended circle.

When asked about his role at the convention, Kennedy and his spokesmen will dutifully give some variation of "this is John Kerry's convention." But people close to Kennedy say he views the Boston convention as a career capstone, and at least two Kerry advisers wonder if Kennedy will stay sufficiently in the background.

"My father's the senior senator," Patrick Kennedy says. "He has every right to feel as if, with all the contributions he's made, with all he's done, in some respect he should be the center of attention" at the convention. "But it shows you that he knows this isn't all about him."

"I don't think there's a jot of jealousy or anxiety to anything he's doing now," says Sen. Chuck Schumer (D-N.Y.). "He's totally at peace with who he is, where he is, and his role in the U.S. Senate and in America."

Kennedy has been trying to lose weight for the convention. "I just weighed myself this morning," he says, depositing his poop bag in the garbage can. "And I'm where I want to be."

Which is?

"Where I want to be."

A Storied Life

Kennedy is sprawled in a chair outside the Senate's Radio and Television Gallery. He is waiting for a news conference in which a group of senators will discuss the patients' bill of rights, which would allow patients to sue HMOs for refusing to treat them.

The group includes Sen. John McCain (R-Ariz.) and eventual vice presidential choice John Edwards.

Kennedy is fascinated by people, relationships between senators, the things that can lubricate collaboration in Washington. He is a student of chemistry.

"It was really interesting to watch the chemistry between Edwards and McCain and how it evolved" during the crafting of the patients' bill of rights, Kennedy says before the news conference. "It just sort of clicked between them."

As he waits at the podium, Kennedy reads to himself from a sheet of talking points. He reads with his whole body -- hunching over the paper, marking it up with a pencil and mouthing the words to himself. He is the first senator to speak, vowing to "stand with the patients" against the big insurance companies and HMOs. He talks loudly, as if he were still in the pre-electricity oratorial age and he's forgotten he has a microphone.

"We're talking about women with breast cancer who need to go into clinical trials," Kennedy booms. "We're talking about children who need specialized help and assistance at critical times in their own life."

The lines about sick kids and women were not in Kennedy's original talking points. The ones his staff prepared were stuffed with facts, figures, abstractions. He demanded real-life examples. People, stories. Kennedy loves stories. He is a story wonk. Job applicants are advised to have a story for each item on their resume when they interview with Kennedy, all the better if it ends with a punch line.

For all his gifts of persuasion and storytelling, Kennedy can be stunningly inarticulate at times. He is prone to umms, muttering asides and mid-sentence detours. This is especially true when he is talking about himself. Asked later if he's bothered by the attacks Republicans have unleashed at him over the years, Kennedy says, "Not, uh, not, uh, really. Having been around for a long time, and having, uh, having had my share of, uh, ups and downs, the rhetoric doesn't really, uh, bother me."

Kennedy's own ups and downs -- his story -- are household lore. Few contemporary figures have lived such momentous stories, so rife with public expectation and tragedy. He was viewed as a future president from the time his brother John was elected president in 1960. Ted was 28 at the time and was elected a senator from Massachusetts as soon as he reached the constitutionally mandated age of 30 in 1962. After his brothers were assassinated, Ted -- still in his thirties -- became both a family patriarch and heir apparent. He ran for president in 1980, but lost badly in the primaries to incumbent Jimmy Carter.

Kennedy was haunted during that campaign -- as he has been throughout his career -- by a 1969 incident in which the senator crashed his car into a pond at Chappaquiddick Island, near Martha's Vineyard, killing his passenger, Mary Jo Kopechne. "Chappaquiddick" remains an all-purpose epithet that's still thrown at Kennedy. (At his son, too: During a House Appropriations Committee debate last month, Rep. Randy "Duke" Cunningham [R-Calif.] said within earshot of Rep. Patrick Kennedy that "maybe we should check into Chappaquiddick." To which Rep. Kennedy said, "You're an idiot.")

Kennedy decided against a second run for president in 1984 and, "after I made that decision, I never looked back," he says. He is fully ensconced in the Senate, one of only five senators in U.S. history to serve more than 40 years. He has championed a litany of liberal causes -- civil rights, care for the poor, elderly and infirm. Kennedy said last month that he would again seek reelection in 2006.

Other than George W. Bush and Bill and Hillary Clinton, there is no politician whose name evokes such fervor on both sides of the political spectrum. Still, Kennedy is widely admired by senators of both parties for his unflagging diligence, grasp of detail and pragmatism. In 42 years, Kennedy has served with 366 senators, and he says the only one he couldn't abide personally was arch-conservative Jesse Helms. "The bottom line is, Kennedy is results-oriented," says McCain. "The man is ready to deal."

Like many senators with whom Kennedy has disagreed over the years, McCain was won over by Kennedy's warmth and his penchant for personal gestures.

In 1999, McCain and Sen. Russell Feingold received a John F. Kennedy Profile in Courage Award for their work on campaign finance reform. The award ceremony, in Boston, included a private dinner the night before that McCain thought he would have to miss because it conflicted with his son Jimmy's 11th birthday.

But Kennedy insisted that McCain come, and he promised that Jimmy would have a good time. "It was amazing," McCain says. "Ted arranged something like three cakes and a special ride on a Coast Guard cutter around Boston Harbor."

Forging a Relationship

There has been much speculation over the years about the chemistry, or lack of it, between Kennedy and Kerry. The Bay State senators are stylistic opposites: Kennedy is a back-slapping legend with a common touch. Kerry is cerebral and reserved to a point that has struck some as standoffish.

Kennedy and Kerry first met in 1971, when Kerry came to Washington for an antiwar demonstration with a group of Vietnam veterans. Kennedy had heard a great deal about Kerry, the decorated Navy lieutenant who had been organizing veterans against the war. Kennedy ventured down to meet Kerry, and the two spent several hours talking. Kennedy arranged to have 100 of Kerry's fellow protesters admitted to a Senate hearing room to witness Kerry's landmark testimony before the Senate Foreign Relations Committee.

As Kerry gained experience and stature, he would occasionally enjoy tweaking Kennedy. In 1997, Kerry moved his office to the third floor of the Russell Building, next to Kennedy's.

"I'll have a balcony off the side, just like Teddy," a longtime aide recalls him saying. "It'll drive him crazy."

In the late 1990s, when Kerry parked his car in a space that was thought to be reserved for the disabled, Kennedy staffers alerted the Boston newspapers.

Both senators deny their relationship has ever been strained, particularly Kerry, who seems sick of discussing the topic.

"I think way too much has been said about that," Kerry says. "I think people have that completely wrong." He says any tension was much more evident at the staff level.

The men have socialized more in recent years. Both were divorced in the 1980s and remarried in the 1990s -- Kennedy to Victoria Reggie in 1992, Kerry to Teresa Heinz in 1995. Heinz and Reggie hit it off immediately, which friends say has helped build a closer relationship between their husbands.

Kennedy endorsed Kerry in January of last year. He has stumped and raised money for Kerry in Iowa and New Hampshire, as well as in Maine, Michigan, Arizona, New Mexico, Wisconsin, Florida and Illinois. When Kerry was floundering in the polls last year, Kennedy made a surprise visit to Kerry's campaign headquarters to boost morale. He recommended that Kerry hire his chief of staff, Cahill, whom many credit with overseeing his turnaround.

In the early primary days, Kennedy served as a handy foil for Kerry on the stump. When Kennedy appeared with him in Iowa and New Hampshire, Kerry would delightedly recount his years of second-fiddle status.

"Someone asked me what it felt like, whether it was really hard to live in the shadow of Ted Kennedy," Kerry said at a January rally in Davenport, Iowa. "He asked me what it was like to know that in all my life, I would never have an amazing legislative record like Ted Kennedy. He asked me if I was jealous of the fact that I was following a living legend.

"And it was Teddy who asked me that."

Kerry told this story at several events. It always drew laughs, especially from Kennedy.

'Just Keep Moving'

Kennedy is at his most animated when giving a tour of his museum-like office.

"When I was born, Hoover sent flowers," Kennedy says, pointing out that his mother received the accompanying letter from the president with 5 cents postage due. He notes this with a fresh burst of revelation, as if he were just discovering the "postage due" stamp and hasn't led thousands of visitors on this tour already.

"This is a letter from my brother Jack to my mother when I was born," he says. "It's the night before exams, so I'll write you Wednesday," Kennedy reads from the letter. "PS -- can I be godfather to the baby?"

Kennedy says he never thinks about whether he'd trade his 42 years in the Senate for one four-year term in the White House. This is one of those questions that Kennedy answers with a dismissive mutter that's barely audible and even less decipherable. He sputters something about "looking forward, not back."

Patrick Kennedy says his father is prone to "Irish melancholy." Given the tragedies he has endured, it would be easy for him to lapse into "paralyzing despair," Patrick says. "He has a philosophy of living that just says, 'Keep moving. If things aren't going well, just keep moving because they'll eventually change.' "

In several discussions with the senator in June, Kennedy comes close to crying -- or actually cries -- on many occasions.

This includes when he shows you a photo of his beloved sailboat, Mya, that was damaged when it washed up on a Cape Cod beach. "The man sailing the boat caught hypothermia, lost his judgment and put the thing on the beach," Kennedy says. "See that beautiful boat on the beach? It's enough to make you cry."

Kennedy's eyes moisten when he talks about Pfc. John D. Hart, 20, of Bedford, Mass., who was killed in Iraq last October.

Kennedy attended his funeral at Arlington National Cemetery and says he heard taps in the distance about eight or nine times in a span of 45 minutes.

"You're there, you get caught up in the emotion, and you know what's going on," Kennedy says, wiping away another tear.

Kennedy and his staff have worked with Hart's father to ensure that military Humvees are equipped with bulletproof shielding, which might have saved Hart when his convoy was ambushed near Kirkuk. When Kennedy visited a military armor plant in Pittsfield, Mass., last month, Brian and Alma Hart drove 21/2 hours to thank him.

"These people have suffered as much as people can suffer, the loss of a child," Kennedy says, his voice trembling. "And they've turned this grief into the ultimate love of country, with all the work they've put in on this issue. . . . Nothing could mean more to me than this. And I'm just going to tell you, promise you, the only thing I can. That we're going to keep on going, keep on going."

Early in the Bush administration, Kennedy seemed to have developed chemistry with the president. "I thought we were cooking along there for a while," Kennedy says. Bush invited Kennedy to the White House a few days after his inauguration to discuss education and, a few weeks later, legislation on disabilities. Kennedy attended a White House screening of "Thirteen Days," a movie about the Cuban missile crisis. Kennedy was grateful to Bush for naming the Justice Department's headquarters after his brother Robert in 2001. He praised the president's "message of hope, strength and compassion" after the Sept. 11, 2001, attacks.

They worked together on the 2001 education bill -- the celebrated No Child Left Behind Act -- that required testing of children in grades 3 through 8. Kennedy went along after the president assured him that the federal government would provide states with the funding to comply with it. But Kennedy was stung when the White House asked for considerably less money for state funding than the bill authorizes.

Last year, Kennedy and the White House worked together on a bill to reform Medicare. Kennedy's involvement allowed Bush to get the support of several key Senate Democrats. But Kennedy himself wound up opposing it . He said that it was "the first step of a total dismantling of Medicare" and that 9 million seniors would be worse off because of the legislation.

"I think Ted made some assumptions that he was comfortable with the Bush family," says Sen. Christopher Dodd (D-Conn.). That affinity dates to the first Bush administration. "There was a lot of disagreement on issues but a basic stylistic compatibility," Dodd says of Kennedy and George H.W. Bush. Former president Bush presented Kennedy with the third annual George Bush Award for Excellence in Public Service at a ceremony in College Station, Tex., last November.

"So I think Ted went into this administration with the assumption that he could work with this guy," Dodd says. "And my sense is he's been personally burned and injured by failure of No Child Left Behind, and especially Medicare."

Kennedy's sharpest public criticism of Bush has been over Iraq, a war that he called "a fraud . . . cooked up in Texas" to advance the president's political standing. He accused the administration of "bribing" foreign nations to send troops to Iraq. In a speech on the Senate floor, Kennedy accused the administration of telling "lie after lie after lie after lie." Last month, Kennedy called Iraq "one of the worst blunders in the history of U.S. foreign policy."

Bush accused Kennedy of "uncivil" behavior, and Andrew Card, the White House chief of staff, called Kennedy to complain. "You don't have to get this kind of intense," Card said, according to Kennedy.

"I said, 'Well you don't have to get us involved in war.' "

Former senator Alan Simpson, a Wyoming Republican and a close Kennedy friend, says his former colleague risks marginalizing himself with his invective.

"He's been saying some vicious and nasty stuff," Simpson says. "I'm appalled. These quotes are just plain nasty and, frankly, out of character for Ted."

Told of this, Kennedy shakes his head and laughs. "These issues make a great deal of difference to me," he says. "I think they're defining issues. War and peace, education, children, these are things I've worked on over a long time." Kennedy leans forward in his chair. His worn eyes bulge slightly, as if Simpson's challenge has raised him to a higher level of wakefulness.

Kennedy says he has nothing against the president personally. He has had no contact with Bush since the Medicare bill passed, with the exception of a brief encounter at a St. Patrick's Day reception. The president asked Kennedy if he'd lost weight.

"Yeah, I've been out campaigning," Kennedy said.

Bush told him not to lose any more weight.

Ted Kennedy with John Kerry at a campaign rally in New Hampshire in January. "It's been unbelievable to me, above and beyond what I would have ever expected," Kerry says of Kennedy's support.The senator plays ball with Splash, one of his two Portuguese water dogs, near the FDR Memorial, a frequent event that includes cleaning up after them. Kennedy draws a laugh from John Kerry and the crowd at a rally in Iowa in January, above left, and introduces him at a Boston fundraiser in April, above. Although the depth of their relationship has been the source of much speculation, Kennedy's campaign help dates back 20 years, when Kerry was making his first run for the U.S. Senate.