Her role as swing justice has made her the most powerful woman in America.

Understanding Justice O'Connor's pivotal position requires a little history.

When Justice O'Connor joined the court, Roe v. Wade (1973) and Regents of the University of California v. Bakke (1978) were the key precedents for abortion and affirmative action, respectively. Neither abortion nor affirmative action had been bitterly partisan at the time these precedents were established. When Roe v. Wade struck down state anti-abortion laws, the majority opinion was written by Republican Justice Harry Blackmun and supported by four of the court's five Democrats and three of its four Republicans.

Five years later, when Bakke was decided, the controlling opinion was written by Lewis Powell, a Southern Democrat appointed by a Republican President, Richard Nixon. Justice Powell staked out a middle ground in the affirmative action debate. His opinion was joined by four Republicans in rejecting racial quotas and joined by four Democrats in permitting race to be considered.

In the decades since Roe and Bakke, opposition to abortion has become a central tenet of Republican ideology, and support for affirmative action has become more clearly associated with Democrats. In the same span of time, the Republican Party has achieved control of both Congress and the White House, and the number of Democrats on the Supreme Court has been reduced to two. With an overwhelming tide of partisan sentiment running against abortion and affirmative action, one might reasonably have expected Republicans on the court to write the obituaries for both. Surprisingly, that has not happened, and Sandra Day O'Connor is the primary reason why.

In 1992, when Roe v. Wade was expected to be overturned, Republican justices O'Connor, Anthony Kennedy and David Souter joined the court's two Democrats to rule that "the essential holding of Roe v. Wade should be retained and once again reaffirmed." Then on Monday, when many anticipated the court would put an end to affirmative action, Justice O'Connor again rode to the rescue. Writing for a bare majority, O'Connor concluded that state universities have "a compelling interest in attaining a diverse student body," and that race may continue to be taken into account to that end. She could as easily have said, "The essential holding of Regents v. Bakke should be retained and once again reaffirmed."

Thus, the opinion of Justice Sandra Day O'Connor has become the pivotal opinion for the preservation of a constitutional right to abortion and for the preservation of affirmative action programs in higher education admissions. In each case Justice O'Connor is out of step with the views of President Bush and of most Congressional Republicans.

That each decision rests on a majority of 5 to 4 would be sufficient to render these decisions precarious and our understanding of the Constitution unstable, but it is widely rumored that the pivotal justice is about to announce her retirement. With the constitutionality of both abortion and affirmative action dependent upon her vote and supported by her opinion, Justice O'Connor's retirement will set the stage for the most consequential Supreme Court nomination in decades.

President Bush can be expected to nominate an individual who would reverse both decisions. The battle over confirmation by the Senate may well be the most acrimonious in a generation, and the process itself is sure to receive much criticism. It won't be a pretty picture, but perhaps the media firestorm, which is assured, will serve to alert Americans generally that the woman or man chosen to succeed Sandra Day O'Connor will single-handedly control the meaning of the Constitution with respect to abortion and affirmative action.

Craig W. Allin teaches constitutional law at Cornell College in Mount Vernon.