"This is terrible." According to Newsweek, that is what Justice Sandra Day O'Connor said at a party on election night in 2000, when Al Gore seemed to have won. Her husband reportedly went on to say that the Supreme Court justice wanted to retire, but would not do so if Mr. Gore would choose her replacement.

In his 2003 book Deciding to Leave: The Politics of Retirement From the United States Supreme Court (State University of New York Press), Artemus Ward, an assistant professor of political science at Northern Illinois University, reports that partisan strategies have become a routine part of Supreme Court justices' departures, such as that of Justice O'Connor, which she announced this morning.

Following are Mr. Ward's comments on this morning's announcement:

Q. How common is it for the justices to calculate their exits in the way that Justice O'Connor reportedly has?

A. It's become incredibly common. In the 1950s Congress expanded the retirement benefits for federal judges and made it more attractive to leave the bench. Some justices have taken advantage of that. But of course an unintended consequence of that, which Congress did not foresee, is that it's given justices longer and longer windows within which to time their retirements to coincide with a favorable administration. Historically, there were no retirement benefits, so justices tended to stay on the court until they died.

When you think that justices spend their entire careers building up a certain type of jurisprudence, it wouldn't make sense for them to retire under a president who disagrees with them. That's why there's no speculation now that Justice Stevens will retire, even though he's 85. Here's a guy who, even though he's a Republican, has been a solid leader of the court's liberal bloc.

Q. Should the justices take advantage of those retirement benefits? Is there evidence that some stay on the court even after their mental capacity has slipped?

A. Yes, that's a major concern. The example that everyone talks about is Thurgood Marshall, but there are others. Justice Marshall retired under a Republican president, but he didn't want to. He left only after it became clear that he wasn't mentally able to keep up with the court's work....