With the long-expected announcement by Justice John Paul Stevens that he will retire by July, the coming summer could be dominated by a big confirmation battle — or perhaps just enlivened by a little skirmish, if President Obama picks a relatively uncontroversial nominee.

Many Republicans are spoiling for a fight to rev up their base for the coming elections. Some would depict any Obama nominee as an ultra-liberal eager to push the Court to the left, legislate from the bench, impose gay marriage by judicial decree, strip "under God" from the Pledge of Allegiance, invent welfare rights, require government-funded abortions, and free terrorists.

But, in fact, none — or at most one — of the four brainy and well-qualified public servants at the top of the shortlists that have made their way into the media from inside sources seems likely to move the Court left.

None of the four is clearly more liberal than Stevens, who is in turn a lot less liberal than, say, the late Justices William Brennan or Thurgood Marshall.

Stevens, who will still have one of the best minds on the Court when he turns 90 on April 20, has long insisted that he remains the old-fashioned judicial conservative and moderate Republican he was when President Ford appointed him in 1975. But the leftward drift of his opinions over the years has made him the senior member of the four-justice liberal bloc.

The four shortlisters are Solicitor General Elena Kagan; federal Appeals Court Judges Diane Wood of Chicago and Merrick Garland of the District of Columbia; and (though some count her out) Homeland Security Secretary Janet Napolitano. President Obama interviewed Kagan, Wood, and Napolitano last spring before choosing Sonia Sotomayor, an Appeals Court judge, to succeed Justice David Souter.

It would be hard for Senate Republicans to justify or sustain a filibuster against any of these four, based on what’s known about them. Indeed, Kagan, Garland, Napolitano, and arguably Wood have less problematic paper trails than Sotomayor, whom the Senate confirmed last summer on a 68-31 vote, with lots of complaining but no filibuster.

Democrats (including then-Sen. Obama) tried to filibuster Justice Samuel Alito in 2006, but the Senate voted 72-25 to break the filibuster and then 58-42 to confirm him. This even though Democrats then held 45 seats — four more than Republicans hold now — and even though Alito was clearly more conservative than Justice Sandra Day O’Connor, his predecessor.

If the president’s priority were to seize his last chance to get a crusading liberal onto the Court before the expected Democratic losses in November, he might choose State Department legal adviser Harold Koh or Stanford law professor Pam Karlan. Other possibilities include Sen. Amy Klobuchar of Minnesota, Michigan Gov. Jennifer Granholm, and Massachusetts Gov. Deval Patrick, all Democrats.

This year, the political pressure to pick another woman or a person of color is not as great as it was when Obama nominated Sonia Sotomayor.

But Obama knows that a big confirmation battle could deplete his political capital and make it much harder to get his proposed legislation on climate change and other matters through Congress. For their part, Senate Judiciary Committee Democrats Charles Schumer of New York and Arlen Specter of Pennsylvania have said they want to avoid a big battle.

In addition, although Obama surely would not pick a conservative, the former law professor does not appear to share some supporters’ passion for a strong left-liberal theorist who could someday lead the charge but who would be hard to sell now to the independent voters whose support the president seeks to reclaim.

Here are sketches of the four candidates on the shortlist:

• Elena Kagan. The solicitor general is the "prohibitive front-runner," wrote Tom Goldstein, a leading Supreme Court litigator and the founder of Scotusblog, in a widely read February 23 piece on his website. I would strike "prohibitive."

Kagan’s assets include her outstanding record as a professor and dean at Harvard Law School, where she brought in some conservative professors and calmed the school’s politically contentious faculty; her experience as a domestic policy aide in the Clinton White House; her age (only 49); and — crucially — her careful avoidance of a paper trail of controversial statements for critics to attack.

Indeed, Goldstein wrote, "I don’t know anyone who has had a conversation with her in which she expressed a personal conviction on a question of constitutional law in the past decade."

The one issue that could slow down Kagan’s confirmation is her impassioned effort as dean to bar military recruiting on campus to protest the law banning openly gay people from serving in the military, which she called "a moral injustice of the first order."

Kagan carried this opposition to the point of joining a 2005 amicus brief whose strained interpretation of a law denying federal funding to institutions that discriminate against military recruiters would — the Supreme Court held in an 8-0 decision — have rendered the statute "largely meaningless." This helps to explain the 31 Republican votes against confirming her as solicitor general.

Many liberal critics are unhappy with Kagan’s arguments as solicitor general supporting the "state secrets" doctrine, detentions without trial, and other broad Obama claims of executive power to fight terrorism — some of them similar to the Bush policies that liberals hate. But their angst would be no obstacle to confirmation.

• Diane Wood. She appears to be the most liberal of the shortlisters and is applauded in progressive circles for going toe-to-toe with the conservative intellectual heavyweights on her court. For this reason, she might have the bumpiest confirmation.

Wood, 59, is highly respected for her intellectual firepower, careful preparation, and clear thinking and expression. She was won praise from some conservative as well as liberal colleagues and from lawyers appearing before her.

Before President Clinton put her on the U.S. Court of Appeals for the 7th Circuit in 1995, she was a University of Chicago law professor — and working mother without benefit of pregnancy leave — and a high-ranking antitrust expert in the Clinton Justice Department.

Some conservatives have assailed her as a hard-left judicial culture warrior whose passion for abortion rights is so strong that (they contend) she has disregarded Supreme Court precedents; and whose writings suggest that she might indeed strip "under God" from the Pledge of Allegiance and make same-sex marriage a constitutional right.

Still, Wood’s overall record may be no more liberal than that of Stevens. She would be confirmed eventually, but she would surely draw more Republican fire than would Kagan or Napolitano, and much more than Garland.

• Merrick Garland. Another intellectually stellar, more moderate Democrat with no apparent land mines in his paper trail and the respect of Republican colleagues and senators alike, the 57-year-old Garland would be the easiest of the four to confirm by far.

In anonymous surveys of lawyers arguing before him, he has won glowing reviews as highly intelligent, open-minded, evenhanded, fair to all parties, and extraordinarily clear and thorough in his opinions.

"After only Judge Wood, D.C. Circuit Judge Merrick Garland is the most respected Democratic appointee now on the bench," as well as the most confirmable, Goldstein wrote. I rank Garland above Wood, given my preference for restrained, moderate consensus-builders. (Disclosure: Garland and I were Harvard Law School classmates and are friends.)

Among Garland’s assets are his 1989 decision to leave a lucrative law partnership to become a federal prosecutor in D.C.; his supervision of a range of major civil, criminal, and national security matters in the Clinton Justice Department, including the initial proceedings against Oklahoma City bomber Timothy McVeigh; and his skill at finding common ground with colleagues across the ideological spectrum. Conservative bench mates have joined logically compelling Garland opinions on ideologically divisive issues.

All of this was not enough to put Garland on Obama’s all-woman shortlist in 2009. This year, the political pressure to pick another woman or a person of color is not as great. But would Obama choose a white male nominee who seems clearly less liberal than Stevens?

• Janet Napolitano. Some media handicappers have written off her prospects because of two much-ridiculed gaffes: saying that "the system worked" after the near-success of a suicide bomber’s attempt to blow up a Detroit-bound airliner on Christmas Day, and speaking earlier of terrorist attacks as "man-caused disasters."

But don’t count the tough, no-nonsense Napolitano out; these lapses were out of character. Obama thinks highly of her, and "if the president is looking for someone who is not a Court of Appeals judge like all current members of the Court, she would be at the top of the list," thanks to her broad political experience, says a source familiar with the selection process and Obama’s thinking.

Before taking over at Homeland Security, the 52-year-old Napolitano was a federal prosecutor, then Clinton’s U.S. attorney in Arizona, and subsequently the elected attorney general and governor of Arizona. She worked effectively with, and often against, the Republican state Legislature, and she won re-election by a wide margin in 2006 by taking centrist, tough-on-crime positions and pushing programs for children that appealed to Republican women.

Some Court-watchers complain that these four possibilities are unexciting, even boring. In my view, that’s a plus.

This article appeared in the Saturday, April 10, 2010 edition of National Journal.