Justice Sandra Day O'Connor's retirement leaves a hole at the center of the Supreme Court and, in a sense, at the center of the country.
During her 24-year tenure, the Republican and Democratic parties came increasingly under the influence of their ideological cores, and Washington grew deeply polarized between left and right.
But O'Connor remained something of a throwback: a moderate Republican, known as a broker of compromises during her long-ago tenure as Arizona's Senate majority leader, who used her pivotal position on the court to keep the law under which all Americans must live from veering toward any extreme.
On a nine-member court that often mirrored the liberal-conservative split of the larger society, O'Connor repeatedly cast the fifth and deciding vote, not to establish sweeping new constitutional principles but to make law that she thought would make sense to the American people.
The first woman on the court thus became the most powerful woman in the United States -- a fact that was acknowledged even by her conservative rival on the court, Antonin Scalia, who said in a statement yesterday that "she has become a star. The statistics show that during her tenure she shaped the jurisprudence of this Court more than any other Associate Justice."
O'Connor was guided not only by her political fingertips. She had a deep-rooted pragmatic sensibility that owed much to her upbringing on a desolate western cattle ranch -- and rather less to the fixed doctrinal principles contained in law books.
"Justice Scalia said the rule of law is the law of rules," said Eugene Volokh, a former law clerk to O'Connor who teaches constitutional law at the University of California at Los Angeles. "Justice O'Connor's view was that the work of the law is making the law work."
Or, as O'Connor put it in dissenting from a ruling by liberal and conservative colleagues who teamed up to strike down state sentencing guidelines in a 2004 decision, "If indeed the choice is between adopting a balanced case-by-case approach . . . and adopting a rigid rule that destroys everything in its path, I will choose the former."
But when they were not angling for her vote, lawyers of both the left and the right would sometimes complain that her approach introduced too much instability into the law and made too many important issues into guessing games about her intentions.
"We have a living Constitution. Her name is Sandra Day O'Connor, and thank God she's retiring," Kevin J. "Seamus" Hasson, founder and president of the conservative Becket Fund for Religious Liberty, said yesterday.
"Her support for separation of church and state was not consistent," said Barry W. Lynn, executive director of the liberal Americans United for Separation of Church and State.
In his 1980 GOP presidential campaign, Ronald Reagan, concerned about the pro-Democrat "gender gap" that had opened up among voters, promised that he would name a woman "to one of the first Supreme Court vacancies in my administration."
When Justice Potter Stewart informed the White House in 1981 that he planned to retire, President Reagan asked aides for a list of possible replacements that included women. At the time, there were few women with significant experience on the bench, and not many of them were Republicans. O'Connor, then a little-known 51-year-old judge on Arizona's appeals court, filled the bill.
Though she had been active in the ill-fated 1964 presidential bid of Sen. Barry Goldwater (R-Ariz.) and she had been friends since law school with William H. Rehnquist, the conservative who would later sit next to her on the court, O'Connor was widely known in her home state as a middle-of-the-roader.
In fact, she was elevated to the court of appeals in 1979 by a Democratic governor, Bruce Babbitt.
In the Arizona Senate, she had voted against busing for school integration and opposed gun control. After the Supreme Court overturned state death penalty laws in 1972, O'Connor was a leader of an effort to write a new one for Arizona.
But she had also supported bilingual education, opposed state aid to private religious schools and was a strong advocate of the proposed federal Equal Rights Amendment.
On abortion, she had voted against a ban on state funds for abortions for poor women, and opposed a bill prohibiting abortions at the University of Arizona hospital. At the same time, she voted to give hospital personnel the right to refuse to participate in abortions.
Conservative warnings that this record made her an unreliable vote against Roe v. Wade, the 1973 decision that recognized a constitutional right to abortion, were outweighed by the historical impact of putting a woman on the court, and she won unanimous confirmation in the Senate.
O'Connor was surprised by her selection and, initially, daunted by the challenges of a court where she had never so much as witnessed an argument before her first day at work in October 1981.
"One of my most poignant memories in life was the day her commission was read to her in the presence of the president and the members of Congress and she put on her robe and ascended to the bench," said Theodore B. Olson, who argued many cases before O'Connor as a private lawyer and as solicitor general of the United States under President Bush.
But, characteristically for a woman who had overcome law firms' refusal to hire her after graduation from Stanford Law School in the early 1950s, she plunged into the work and quickly made a mark.
She became a close friend of Justice Lewis F. Powell, then a moderate conservative on the court who, three years before O'Connor's arrival, had tried to define a centrist answer to the bitterly disputed Bakke affirmative-action case, suggesting that racial quotas in university admissions were unconstitutional but that using race as a "plus factor" to help qualified minorities was not.
The hallmark of O'Connor's style was what University of Chicago law professor Cass R. Sunstein called "judicial minimalism." She would decide cases incrementally, making no more law than was necessary to deal with the particular set of facts before her.
Her opinions were an exercise in keeping her options open; they would often contain qualifications or exceptions that reappeared in later cases as her rationale for reaching a seemingly different result on a similar issue.
And, when she was the fifth member of a majority, she sometimes issued a concurring opinion that articulated a narrower basis for the decision -- and became the de facto controlling precedent.
In 1985, O'Connor articulated a case-by-case "endorsement" test for deciding whether a given governmental action in support of religion violated the Constitution. According to O'Connor, the First Amendment's ban on the establishment of an official religion meant that governments could not advance or endorse religion.
The phrase "under God" in the Pledge of Allegiance, and a Cleveland program that gave parents government money to send their children to parochial schools, passed constitutional muster with her, while the posting of the Ten Commandments in a county courthouse or on the Texas Capitol grounds could not.
She generally voted for conservative positions on crime, economic regulation and, especially, states' rights. Among the federal laws O'Connor voted to strike down as violating state sovereignty were one that barred the carrying of a firearm within 1,000 yards of a school, a provision of the Americans With Disabilities Act permitting disabled state employees to sue their bosses for discrimination, and a provision of the Violence Against Women Act that let rape victims sue their attackers in federal court.
In her last term on the court, O'Connor dissented in a 6 to 3 ruling that gave the federal government the power to override California's state law permitting the use of homegrown "medical marijuana."
Noting that she would have voted against legal marijuana if she were a Californian herself, O'Connor faulted the court for "stifl[ing] an express choice by some States, concerned for the lives and liberties of their people, to regulate medical marijuana differently."
Yet O'Connor's backing for states' rights was not unlimited. She would not let it become a means to roll back what she saw as the core social advancements of the 1960s and '70s.
Two years ago, she voted with the majority to uphold the right to sue state employers for violating the federal Family and Medical Leave Act, in a case widely seen as a test of gender equality in the workplace.
In 2004, she joined the liberals in a 5 to 4 ruling that said states could be sued under the disabilities act if they fail to make their courthouses accessible to the handicapped.
And on abortion and race, O'Connor, after expressing many Americans' second thoughts about the social changes of the '60s and '70s, ultimately decided not to undo them.
In 1983, the court, citing Roe v. Wade, struck down an Akron, Ohio, ordinance that put regulations on abortion, including a required 24-hour waiting period. O'Connor dissented, offering some critical words about Roe.
She heartened conservatives again in 1986 and 1989, when she voted to uphold abortion regulations in Pennsylvania and Missouri.
But in 1992, when appointees of Reagan and President George H.W. Bush seemed to have a majority to overturn Roe, O'Connor hesitated.
She invoked an alternative constitutional balancing test that she had hinted at in early opinions: that the right to abortion could be limited only as long as the state did not impose an "undue burden" on it.
She voted to reaffirm Roe, striking down the Pennsylvania law's requirement that wives notify their husbands before an abortion.
In 2000, O'Connor was also in the majority when the court ruled, 5 to 4, that a Nebraska law banning late-term abortion violated O'Connor's "undue burden" test. Yet she issued a separate concurring opinion suggesting she would not rule out all efforts to legislate against a procedure that opponents call "partial-birth" abortion.
Justice Harry A. Blackmun, the author of Roe, concluded it was no surprise the Supreme Court's first woman had voted to affirm Roe.
"She is a believer in states' rights in the sense that she feels an issue of this general nature should be left to the state legislatures and not be federally constitutionalized," Blackmun said in an oral history of his years on the court that was published early last year. But, he added, "she is a woman and may fear somewhat any accusation of being a traitor to her sex. Some women's organizations would so conclude."
Whatever her private motivations, O'Connor's ambivalent embrace of Roe was consistent with the American public's. According to Gallup polls going back to 1992, a significant majority opposes "completely" overturning Roe; according to a 2004 Washington Post-ABC News poll, only 17 percent of Americans think abortion should always be illegal, while only 21 percent think it should always be legal.
During the 1980s and '90s, O'Connor helped the court establish the rule that affirmative action should be subjected to the same "strict scrutiny" as discrimination against minorities. As O'Connor saw it, only "compelling" governmental goals could justify affirmative action, and even then programs would have to be "narrowly tailored."
Yet for all her reservations about affirmative action, O'Connor never ruled it out. In her 1995 opinion enshrining "strict scrutiny" of affirmative action, for example, she insisted that the "unhappy persistence of both the practice and the lingering effects of racial discrimination against minority groups in this country is an unfortunate reality, and government is not disqualified from acting in response to it."
In 2003, when white students challenged their denial of admission in favor of black students with lower test scores at the University of Michigan, O'Connor backed the university.
Diversity in higher education could, indeed, qualify as a compelling state interest, she wrote for a five-member majority consisting of her and the court's four most liberal members. As long as a school did not mechanically assign minorities' applications extra points, but gave all students individualized consideration, its approach would be constitutional under Powell's opinion in Bakke.
Her opinion took sympathetic note of the views of large corporations, university deans and retired military officers whose friend-of-the-court briefs called affirmative action necessary to educate a racially integrated elite -- and, by implication, to preserve the stability and legitimacy of the American meritocracy. Her only nod to critics of the programs was her expressed wish that they might no longer be necessary in 25 years.
Once again, O'Connor's position -- diversity, yes, quotas, no -- was roughly in line with public opinion.
In a Fox News poll published shortly after the affirmative-action decision, O'Connor ranked as the Supreme Court justice Americans "most admire or agree with."
O'Connor testifies before the Senate Judiciary Committee at a confirmation hearing in September 1981.
The associate justices, from left: David H. Souter, Clarence Thomas, O'Connor, Antonin Scalia, Ruth Bader Ginsburg, John Paul Stevens, Anthony M. Kennedy and Stephen G. Breyer.