Abstract: When Justices William Rehnquist and Sandra Day O’Connor left the bench last year, conservatives were in an anxious mood: though pleased at the prospect of shifting the Supreme Court to the right, they were worried by the record of past Republican appointments. The refrain in conservative commentary, repeated with special intensity during the Harriet Miers affair, was: Not another Souter. Not another Kennedy. Not another O’Connor. And they might have added: Not another Blackmun. Not another Stevens. Not another Warren. They were right to be concerned. While there have been a number of relatively reliable conservative justices over the years—Antonin Scalia, Clarence Thomas, and Rehnquist being prime examples—and some important right-shifting exceptions—notably Felix Frankfurter, appointed by Franklin D. Roosevelt, and Byron White, appointed by John F. Kennedy—the tendency in recent decades to drift leftward has been strong enough to gain both popular and scholarly attention. Indeed, Larry J. Sabato, the director of the University of Virginia Center for Politics, has suggested that about one quarter of confirmed nominees over the last half century have wound up “evolving from conservative to moderate or liberal.”