Now that Supreme Court Justice John Paul Stevens has announced his intention to retire this summer, commentators are already speculating about who the President might choose to replace him. (Watch an AP report about Stevens' retirement.) Although Stevens was nominated by Gerald Ford, he moved leftwards during his 35 years on the court to become the de facto head of its liberal wing. So who might Obama name as Stevens' replacement? A look at five of the leading contenders:

Elena Kagan
Who? Solicitor General of the US, former Dean of Harvard Law School. Interviewed by Obama before he appointed Sonia Sotomayor to the court, Kagan is "widely considered the front-runner" to replace Stevens, says the Huffington Post.
Why she's a favorite: The first female solicitor general, Kagan has experience of arguing in front of the court. She has a reputation for "bridging disagreements between liberal and conservative" thinkers, says Mark Sherman at Real Clear Politics, which makes her a good moderate choice.
What the GOP will say: Republicans are reportedly concerned about her lack of courtroom experience, and the fact she opposed on-campus military recruiting at Harvard. Her appointment to solicitor general was opposed by 31 Republican senators.

Diane Wood
Who? A judge on the 7th US Circuit Court of Appeals in Chicago, and former deputy assistant attorney general under Bill Clinton. Also interviewed by Obama before the Sotomayor appointment.
Why she's a favorite: Wood has a reputation as an "intellectual jurist willing to take on her more conservative colleagues" on the Chicago appeals court, says Greg Stohr at Bloomberg.
What the GOP will say: Her record on issues such as abortion - pro-choice, she once clerked for Roe vs Wade author Justice Blackmun - "could potentially be used against her," says the Huffington Post.

Merrick Garland
Who? A judge on the US Court of Appeals for the D.C. circuit, and former employee of the Justice Department during Clinton administration
Why he's a favorite: As the Dems' "leading moderate jurist," Garland would be an "easy pick" for the Obama administration, says Gabriel Winant at Salon, if it is seeking to avoid a fight over the nomination.
What the GOP will say: Garland is a "well-respected moderate," says Dahlia Lithwick in Slate, whom the right thinks of as the "best alternative" to Stevens.

Cass Sunstein
Who? The Felix Frankfurter professor of law at Harvard Law School
Why he's a favorite: Academics like Sunstein would bring a "deeply worked-out constitutional vision to the court," says Dahlia Lithwick in Slate.
What the GOP will say: As "one of the most reliable Democrat cheerleaders for Bush/Cheney radicalism," Sunstein's appointment would likely please the GOP, says Glenn Greenwald in Not necessarily, counters Huff Po. His "vast body of work" would likely unearth something leaving him "vulnerable to criticism."

Pamela Karlan
Who? Professor of law at Stanford Law School
Why she's a favorite: A pro-choice liberal, Karlan could "move the court's center significantly leftward," says Dylan Matthews in the Washington Post, if Obama decides to make his mark on the court.
What the GOP will say: That "decidely liberal disposition would likely generate stiff opposition in the Senate," says Huff Po. Karlan is also openly gay, which could "provide an extra hurdle" to jump, says Ashby Jones in the Wall Street Journal.

This piece was originally published April 6, 2010