Vice President-elect Joe Biden leaves an open chairmanship on the Senate Foreign Relations Committee that could end up  being filled by one of the most outspoken critics of the Iraq war.

Sen. Russ Feingold (D-Wisc.), among the chamber’s most liberal members, is the fourth Democrat in line on the committee, behind Biden, Sen. Chris Dodd (Conn.) and Sen. John Kerry (Mass.).

That leaves Feingold, an unapologetic champion of civil liberties and a staunch opponent of the Bush administration’s war in Iraq, next in line. Feingold opposed the war from the start and was the first senator to call for a U.S. troop withdrawal timetable.

Democrats could bypass the Wisconsin senator and choose a more centrist member, such as Sen. Bill Nelson (Fla.), who initially supported the war and could be more open to compromise. But that would rile the party’s left wing.

"It would seem like an extreme move to bypass senators with a great deal more seniority," said Christopher Anders, a senior  legislative counsel for the American Civil Liberties Union (ACLU).

In addition to opposing the war, Feingold has been fiercely critical of the current administration's policies toward terror suspects, which he has viewed as unconstitutional. Feingold earned plaudits from the ACLU for calling for the closing of the prison on Guantanamo Bay for terror suspects and by demanding a stop to the transfer of suspects to countries with less strict standards on torture, a program known as "extraordinary rendition."

And he was the only senator who voted against the anti-terrorism law known as the Patriot Act, in the days after the Sept. 11 terrorist attacks.

"Without any hesitation, [Feingold] would be a terrific chairman," Anders said.

The ACLU would expect Feingold as chairman to conduct oversight hearings of the extraordinary rendition program. The next chairman should also press to close any secret prisons abroad and should make sure that other countries understand that the United States won't engage in or support torture.

He added that the ACLU would feel just as confident with Kerry or Dodd as chairman of the committee.

After Feingold, next in line is Sen. Barbara Boxer (D-Calif.), who is chairwoman of the Senate Environment and Public Works Committee and holds similar views on foreign policy, followed by Sen. Nelson.

Dan Senor, a former Bush administration spokesman in Iraq, said that Democrats should choose Nelson, who had been skeptical of a troop pullout just two years ago.

Senor said that the Senate Democratic leadership and Obama's transition team would have concerns about "a hard-left chairman of important committees that's going to make it harder for Obama to make compromises."

Nelson, unlike Feingold or Boxer, would be more willing to give Obama more flexibility over a troop pullout plan, which the administration may want, Senor said.

"I think [Nelson's] been in the standard Democratic position, which is basically supportive of Obama but not with the  ideological purity that Feingold has," Senor said.

A spokesman for Senate Majority Leader Harry Reid declined to comment on the chairmanship. Offices for Feingold and Nelson didn't return phone calls for the story.