This type of candidate often has been viewed as the safest choice. A contender in this category — and a diversity candidate — would be Judge Diane Wood, of the Chicago-based U.S. Court of Appeals for the 7th Circuit, appointed in 1995 by Clinton. Wood previously worked in the Justice Department's antitrust division and taught at the University of Chicago law school when Obama was on the faculty there.
Another strong candidate in this category, also a woman, would be Sotomayor. She was appointed to a U.S. trial court in 1992 by the first President Bush, and elevated to the appeals court in 1997 by Clinton. She was born and grew up in the Bronx.
The choice of a political figure could signal that the president wants a broader base of experience for a justice tasked with resolving the legal dilemmas of American society. In addition, much of the high court's work involves interpreting the policies of legislators. Someone who has served in elective office would have experience making the laws that are typically at the core of disputes before the court.
"I would hope that he would look beyond the circuit courts of appeals which now populate the Supreme Court and pick someone with greater world experience and diversity," Specter said Sunday on NBC's Meet the Press. "It would be good to get people who know something besides wearing a black robe."
When Clinton had his first opportunity to name a justice, in 1993, he wanted to go with a politician in the mode of Warren. Clinton first considered then-New York governor Mario Cuomo, who declined. Clinton then chose women's rights legal advocate Ginsburg, whom he termed "the Thurgood Marshall" of women's rights, reflecting his interest in a "diversity" model.
Among political figures who could be in the mix now are Michigan Gov. Jennifer Granholm, a former state attorney general who, like Obama, has a Harvard law degree; and Homeland Security Secretary Janet Napolitano, Arizona's former governor and attorney general. Another politician-lawyer is Patrick, also a Harvard law graduate.
The compromise candidate
A compromise candidate could guarantee that a president who has many other pressing items on his domestic agency doesn't get distracted. Obama has stressed the benefit to democracy of a nominee embraced by senators of both parties, rather than one who is politically polarizing.
In 1975, after Watergate, President Ford chose a lawyer with stellar credentials and no political baggage who easily could be confirmed: John Paul Stevens was approved by the Senate, 98-0.
Reagan opted for the opposite of a compromise candidate and took an ideological route with Robert Bork in 1987. The Democrat-controlled Senate rejected the conservative federal judge.
Obama said Friday he will consult with senators of both parties.
"Because federal judges receive lifetime appointments and often serve through the terms of multiple presidents," he wrote in his 2006 book, The Audacity of Hope, "it behooves a president — and benefits our democracy — to find moderate nominees who can garner some measure of bipartisan support."
Yet with nearly 60 Democratic votes in the Senate, Obama is unlikely to have to seriously compromise on his choice. He supports liberal priorities such as abortion rights and affirmative action, and it is likely any nominee would reflect that.
Hatch warned Sunday that he believed Obama's interest in qualities like "empathy" could be code "for an activist judge."