Justice John Paul Stevens turns 90 next month and is expected to announce soon whether he will retire from the Supreme Court and kick off a nomination battle for his replacement. Stevens hired only one law clerk for next fall's term instead of the usual complement of four, setting off speculation he will step down.
Stevens is the leader of the closely divided court's left flank and recently told The New Yorker that he will retire in the next three years -- meaning Democrat Obama would get the chance to name his successor. Supreme Court watchers already have begun drawing up short lists of who might be nominated if he announces in April that he is stepping down before next fall's new term.
That would throw the nomination process into a Washington milieu already rife with partisanship, as Republicans complain about the way Democrats have pushed through health care reform and the parties battle for control of the Senate in November.
The tension between Obama and Roberts began with the Citizens United court decision, which dropped some limits on corporate involvement in political campaign spending. Obama has pointedly criticized the ruling, and Roberts has taken issue with the president calling out the Supreme Court as it sat through the State of the Union speech.
"The Citizens United case was a wake-up call to a lot of ordinary Americans the Supreme Court has a tremendous amount of power," Brina Milikowsky, attorney for the liberal civil rights group Alliance for Justice, told AOL News, predicting great public interest in the nomination process.
Supreme Court observers say the tenor of a nomination battle will be set by whom Obama picks. The White House already has been through the process once when it named Sonia Sotomayor. But that first nomination came when Obama was riding high in public opinion and was helped along by the historic nature of the first Hispanic joining the court.
This time the White House will weigh whether to name another woman or a minority. And it will balance the left wing of the Democratic Party's desire for a liberal like Stevens against the need to win approval in a Senate where a liberal would draw more political flak.
"I do expect there will be substantial push-back on any nominee of the president because that has been the way the Senate has been operating," said Marcia D. Greenberger, head of the liberal National Women's Law Center, noting that lower-court nominations have been held up even when there has been a large majority in the Senate.
But M. Edward Whelan III, head of the conservative Ethics and Public Policy Center, said the first battle will be within the Democratic Party as the left wing presses Obama not to name a moderate. "They're hungry for someone who will be a liberal lion," Whelan said.
Curt Levey, head of the Committee for Justice, which favors judges who interpret the Constitution strictly, says many conservatives are hoping for a debate over judicial activism. But a moderate nominee could take the wind out of the sales of a major nomination battle.
So who's in the running? Here are some possible nominees from the worlds of the federal courts, politics and academia:
U.S. Circuit Court Judge Merrick B. Garland from the Washington, D.C., appeals court, who is 58, is considered a top contender. Levey said conservatives respect him for not approaching the bench with an agenda.
Elena Kagan isn't a judge, but as solicitor general she represents the United States -- and Obama -- before the Supreme Court. Although she comes with less paper trail to dissect, some recent writings are conservative on national security issues, said court watcher Bruce Fein, who served in the Justice Department under President Ronald Reagan.
Kagan, a former Harvard Law School dean, likely would have some support from conservatives. "We all suspect she's quite liberal," Levey said. "But she's also a really nice person. She has reached out to conservatives."
Fifty-nine-year-old U.S. Circuit Court Judge Diane Wood from Chicago, on the other hand, would provoke conservative ire, Levey said, especially because of her views on issues like abortion and religion. "You're just handing the right the type of hot-button social issue Obama had indicated he doesn't want" to raise, Levey said.
Two leading lawyers who have spent years in academia often are mentioned. Cass Sunstein, 55, taught at the University of Chicago Law School and then Harvard Law School and now is serving as Obama's regulatory czar as administrator of the Office of Information and Regulatory Affairs. Human-rights activist Harold Hongju Koh, 55, is serving as legal adviser to the State Department after years at Yale Law School.
Sunstein is well-respected and personally close to fellow Chicagoan Obama, Milikowsky added.
Obama has that said bringing a diversity of experience to the court is important to him, leading to speculation he would name a politician. Govs. Jennifer Granholm of Michigan, 51, and Deval Patrick of Massachusetts, 53, along with Sen. Amy Klobuchar, D-Minn., all have been mentioned. But Fein doubts they have enough judicial background for the job. "To challenge the conservative wing [of the court], you are going to have to have someone with intellectual firepower," he said.
Klobuchar, 49, or Granholm would become the third woman serving on the current court, which would be a new record. Justice Ruth Bader Ginsburg, 77, is the oldest member of the court after Stevens and subject to speculation about when she will retire.
Interior Secretary Ken Salazar, 55, a Hispanic from Colorado, also would add demographic diversity to the court.
Two other Obama Cabinet officials have seen their stars dim in the past year, according to court watchers. Homeland Security Secretary Janet Napolitano, 52, took heat for security lapses after Umar Farouk Abdulmutallab allegedly tried to blow up a Northwest Airlines plane bound for Detroit with a bomb stashed in his underwear. And Attorney General Eric Holder, 59, has been under criticism for other administration decisions on security that Obama might not want to draw attention to in a hearing, Levey said.
Fein puts the odds of a nominee being confirmed by the start of the new term in October at "zero or negative integers." Republicans, he said, will delay the process so they can wait until after the November elections, when the party is expected to pick up more seats in the Senate.
But Whelan said hearings could come as early as July, as they did for Sotomayor. "It's a sensible working assumption that anyone who gets nominated will, in the end, get confirmed. The big question is, at what political cost?"