The news came as a surprise. Souter still seems to be in excellent health, and at 69 he is one of the youngest justices on the court. After he goes, at least two more justices -- both on the liberal side like Souter -- are expected to soon retire too: John Paul Stevens, who is 89, and Ruth Bader Ginsburg, 76, who had cancer surgery last year. All three are liberals, and Stevens, like Souter, was appointed by a Republican president.
Souter could be called "Sununu's folly." Former New Hampshire Gov. John Sununu recommended him as a conservative justice to President George Herbert Walker Bush when he was Bush 41's White House chief of staff. But Souter soon decided that being a conservative judge in his native state was very different from what conservatism had come to mean in Washington, and he didn't like it.
He has been a generally reliable pillar of the liberal wing of the court and a thorn in the side of Republican presidents ever since, and it is striking that he chose to retire so soon after Republican President George W. Bush left office. Stevens and Ginsburg are also widely believed to have hung on despite Stevens' age and Ginsburg's health problems until they could be sure a liberal president would appoint successors who would follow in their ideological footsteps.
The front-runner to succeed Souter appears to be U.S. Judge Sonia Sotomayor, a Hispanic judge on the U.S. Court of Appeals for the 2nd Circuit.
Sotomayor has an excellent record in legal terms, she is a woman, and she is Hispanic. Obama won his sweeping election victory on Nov. 4, 2008, with very strong support from the Hispanic community and from female activists. There is no judge of Hispanic background currently on the court, and the president has also made clear he would like to have another female judge.
Another possibility is Diane Wood, a federal judge in Chicago who was a colleague of Obama at the University of Chicago.
Obama's own solicitor general, Elena Kagan, has also been tipped as a front-runner for the position, but she seems less likely precisely because she has hit the ground running so well for the White House so far. Obama has had more than his share of embarrassments in top-level appointments who had to withdraw, or who have proved controversial lightning rods for widespread criticism like Homeland Security Secretary Janet Napolitano and Treasury Secretary Timothy Geithner. He will want to hang on to the ones like Kagan who are doing well at this early point in his administration. When Ginsburg steps down, Kagan may be the president's choice to succeed her.
Souter's timing is also striking in that it comes right after the president and the ruling Democrats in both houses of Congress are celebrating the defection to their ranks of Pennsylvania's senior senator, Arlen Specter, after more than 28 years as a Republican in the upper chamber. Once comedian Al Franken is finally confirmed as the junior senator from Minnesota after an endless marathon of recounts in his contest against incumbent Sen. Norm Coleman, R-Minn., that will give the Dems their coveted 60-seat majority in the Senate sufficient to cut off any filibusters. And that, in turn, means that the Republican rump in the Senate will be cut off from any effective blocking procedure to prevent Obama pushing through any Supreme Court nominee he likes.
Specter has been a powerful figure on the Senate Judiciary Committee over the decades. He has pledged not to be a rubber stamp for the White House in his new incarnation as a Democrat, and in fact he did vote against the budget this week. But he is very likely to support the nomination of a liberal-leaning Supreme Court justice.
Obama may get to choose three Supreme Court justices during his first couple of years in office, a highly unusual occurrence. If that happens, he will be able to renew the current liberal majority on the court for another generation, but he will not be increasing it, as the justices he will be replacing were all staunch liberals themselves.
But Obama should steel himself for the likelihood that whoever he appoints to succeed Souter or anyone else may surprise and confound him. Over the past 70 years that has happened a remarkable amount of the time to any president who thought he could shape the decisions of America's highest court of law.