Foreign policy and the economy have emerged as the themes of this year's presidential campaign. But in the next four years we're less likely to see another terrorist attack or recession than a different potentially life-changing event: the retirement of a Supreme Court justice. The current crop of justices has been together for a record 10 years. It includes the 84-year-old John Paul Stevens, the oldest member of the court, and others who have had health problems. Given the Rehnquist Court's penchant for 5-4 decisions, a new justice could alter American society for decades.

Whoever wins the White House, it probably won't change the disingenuous pattern of partisan warfare that now takes place surrounding such nominations. Even while battling each other, the two parties collude in promoting a fiction: Both profess, against all evidence and common sense, that they choose and evaluate nominees not on the basis of ideology, but on professional merits. To base one's opposition or support solely on ideology is seen as politicizing the judiciary, the branch of government that's supposed to stand above the messy fray of partisan politics. So party leaders contrive to find extra-political reasons to oppose a nominee. They root their objections in a reputed character flaw, or performance of some unsavory act long ago, or lack of professional merit. Despite the illusions put forward, it's clear that ideology is at work in both appointment and confirmation.

No justice is apt to retire until the election is finished. But when one does, the pattern will reassert itself. Already, President Bush is spoiling for a fight. In his 2000 campaign, he pledged to appoint justices in the mold of Antonin Scalia and Clarence Thomas, the court's most conservative jurists. Last summer, he rebuffed Senate Minority Leader Tom Daschle's idea that he confer with Senate Democrats before selecting any nominee. Some of his choices for appellate court judges -- notably Brett Kavanaugh, whose chief professional distinction has been to help write the Starr Report -- are hard to interpret as anything but acts of partisan aggression. And earlier this month, Bush visited North Carolina and Michigan to blast the Democrats for holding up his lower court appointments.

Senate Democrats, numbering 48, constitute a large enough minority to block any appointment (if they stick together), since it takes 60 senators to end a filibuster and bring a nomination to a vote. During Bush's presidency, Democrats have united to oppose several of Bush's choices. They filibustered last year to block the appointment of Miguel Estrada to the U.S. Court of Appeals for the District of Columbia Circuit. Estrada's conservative views regarding due process rights earned him the opposition of most black and Hispanic groups.

November's election won't change much; neither party is going to gain enough Senate seats to have a filibuster-proof margin. The Democrats, even if they were to regain control, won't be able to do more than obstruct the GOP agenda if Bush wins. And if John Kerry wins? Republicans proved during Bill Clinton's presidency that they, too, can thwart an appellate court nomination. Clinton dodged fights at the Supreme Court level by vetting his potential nominees beforehand with Senate GOP leaders. Still, when Byron White and Harry Blackmun retired, in 1993 and 1994, danger filled the air. Had Clinton followed his heart and nominated former New York governor Mario Cuomo, he would certainly have ignited a firestorm. Instead, he put Ruth Bader Ginsburg and later Stephen G. Breyer on the high court.

Although a few senators have recently begun arguing for letting friends or foes of a nominee frame their support or objections in honestly ideological terms, they have yet to alter the dynamic. That's because five deep historical developments -- the decline of the imperial presidency, the prevalence of divided government, the rise of expertise, the advent of identity politics and the emergence of a culture of scandal -- have conspired over the last generation to bring us to where we are today.

This unacknowledged partisanship was not the norm for court appointments in earlier eras. In the nation's first century, senators were deeply involved in the appointments, often objecting to a president's nominees for unabashedly political reasons. Between 1789 and 1894, 22 of 81 presidential Supreme Court nominees failed to reach the bench. They were either rejected, withdrawn or left unacted upon by the Senate. The reasons senators gave were sometimes baldly political. For example, George Washington's nomination of John Rutledge to be chief justice in 1795 foundered because Rutledge opposed the newly negotiated Jay Treaty with Great Britain. Nathan Clifford, James Buchanan's choice for the bench in 1858, was rejected for being too pro-slavery. And radical Senate Republicans beat back Ulysses S. Grant's effort in 1870 to place on the court Ebenezer Hoar, who had opposed the impeachment of Andrew Johnson.

In the 20th century, a different pattern emerged. Senators mostly deferred to the president's wishes. From 1895 to 1968, only one high court nominee -- John J. Parker, in 1930 -- met defeat. Although a few others faced some rough weather, the strong presidency that emerged with William McKinley and Theodore Roosevelt allowed the chief executive generally to shape the Supreme Court.

The collapse of the unchallenged presidential prerogative did not start, as is often said with Ronald Reagan's ill-fated 1987 nomination of Robert Bork. Rather, it began in 1968, when an alliance of Republicans and Southern Democrats, furious about the liberal rulings of the Warren Court, filibustered to keep Lyndon Johnson from elevating his friend Abe Fortas to the chief justiceship. (It's often recalled that Fortas was blocked because of shady financial dealings, but those arrangements didn't fully emerge until the next year, when they precipitated his resignation altogether.) Since the Fortas imbroglio, most presidents have faced difficulty in getting their appointments through the Senate. Richard Nixon lost two battles (Clement Haynsworth and G. Harrold Carswell) and so did Reagan (Bork and Douglas Ginsburg). And both those presidents had trouble confirming William Rehnquist, first to the court and then as chief justice. George H.W. Bush won a fierce fight over Clarence Thomas. All along, ideological warfare -- under the increasingly untenable guise of a debate on the merits -- intensified.

Several profound shifts in American culture combined to create this new politics of appointments. First, the late 1960s and early '70s witnessed a broad assault on the presidency from the New Left and the New Right alike, and, with the Nixon administration's abuses of power, liberals also began to fear an "imperial presidency." Responding to such concerns, senators revived their advise-and-consent mandate as a way to check executive power.

Divided government also shaped the new dynamic. Nixon was the first president since 1848 to take office with the opposition party controlling both houses of Congress, and many Democrats, angry over Fortas's treatment, resolved not to let the new administration steer the high court into conservative terrain. Reagan, the first Bush and Clinton also lacked Senate majorities, complicating nominations.

If senators felt emboldened to oppose appointments, they hesitated to do so on openly political grounds. This reluctance stemmed partly from a third historical trend: the century-long rise in respect for expertise, which put an emphasis on finding nominees with distinguished backgrounds. Since the Progressive Era, all disciplines, including law, had grown professionalized, with guild members resting their authority on their access to a rarefied body of knowledge and set of skills. (This development led Dwight D. Eisenhower to ask the American Bar Association to rate his judicial nominees, a practice that seemed permanent until the current Bush administration abandoned it.) When Carswell was derided as "mediocre," Republican Sen. Roman Hruska's much-quoted defense -- that mediocre Americans, too, deserved representation on the court -- seemed laughably absurd because the notion of professional excellence had become so entrenched.

Simultaneously, multiculturalism swept across American society. As ethnic, religious, racial and gender consciousness grew, politicians eyed gains that could result from making appointments from key constituencies. LBJ won praise for naming Thurgood Marshall, the first African American justice, and Nixon's deliberations were consumed by questions about how the gender, religion and ethnicity of nominees would play. By the 1980s, conservative politicians realized that being female or black or Hispanic could inoculate nominees against liberal opposition. (When it hasn't, as with the recent appellate court nominations of Estrada and William Pryor, some Republicans charged, preposterously, that the Democrats opposed these men because they were, respectively, Latino and Catholic.) Bush is said to be considering naming a conservative Latino, such as White House Counsel Alberto Gonzales, to the Supreme Court. Ethnic identity, too, has become a talisman.

Expertise and identity became innovations in public relations -- ways of winning the battle by setting the terms of debate. Senators responded with innovations of their own. Notably, the enthusiasm for personal scandal that engulfed politics in the Watergate era provided a way to shoot down unpalatable nominees without invoking ideology. Since Fortas, nominations have turned -- superficially -- on questions of alleged financial impropriety (Haynsworth), racist behavior (Carswell, Rehnquist), sexual harassment (Thomas), drug use (Ginsburg), blindness to conflicts of interests (Haynsworth, Carswell) or other scandals, real or inflated.

Even the apparent exception to this rule -- the 1987 defeat of Bork -- reinforced the unspoken ban on ideology. Bork's critics described him not as too conservative, but as "out of the mainstream." "I supported Justices O'Connor and Scalia as well as Chief Justice Rehnquist," Sen. David Pryor (D-Ark.) said. "But the question of Robert Bork is not an issue of a person being conservative or liberal, Republican or Democrat. It is a larger question of temperament and understanding." His foes seemed to be decrying the bearded nominee's character or even his sanity, rather than his opinions. (Bork asked the White House if he should sacrifice the beard for the team, but it was decided that shaving off a 20-year-old personal trademark would attract more criticism than the facial hair.)

Bush spoke in what has become familiar code during his July 7 campaign stop in North Carolina. "When the nominees come before people in my administration, we don't say, what is your specific position on that issue or another issue. What we say to the person is, what is your judicial temperament?" Bush said. "And I don't believe in litmus tests . . . . I do believe in making sure that we share a philosophy."

It's perfectly natural that Supreme Court appointments should be political issues, and it's time to stop pretending otherwise. Justices do not shed their politics when they join the bench. Senators shouldn't be embarrassed to say that they care whether the court is liberal or moderate or conservative. And candidates for president should be pressed to talk about it a lot more.

David Greenberg writes the "History Lesson" column for the online magazine Slate and teaches at Rutgers University. He is the author of "Nixon's Shadow: The History of an Image" (W.W. Norton).