John Kerry

When Lugar leaves, the most likely choice to replace Lugar is Corker, a Tennessee businessman who like Lugar, opposed the war in Libya and opposes intervention in Syria. But Corker's foreign policy stance is even more wary of using U.S. power in foreign lands. He said earlier this year he doesn't even believe the Syrian revolution is about "democracy."

Corker was on the fence during much of the New START debate. He felt the treaty wasn't very significant in terms of nuclear reductions, and used the negotiations within Congress more as chance to secure funding for nuclear facilities, some of which are in his state. Corker is very effective at defending funds for nuclear modernization and stockpile maintenance.

Corker doesn't have a firm position on what to do in Afghanistan and he wasn't particularly vocal on the U.S. withdrawal from Iraq. He's seen on Capitol Hill as someone would have a bit of a learning curve ahead of him were he to become SFRC chairman or ranking member.

Behind the scenes, Corker has a very active foreign policy staff that is said by Hill sources to not get along well with Lugar's staff. If Corker takes over as lead Republican on the committee, there could be a house cleaning on the staff side.

But Corker's accession is not assured. The Republican committee members have the power to vote for whomever they want. In fact, after the 2010 election, there was an effort to vote Lugar out of the ranking member's position, but Lugar prevailed by a slim margin.

For some Republicans both on and off Capitol Hill, Corker is seen as neither aggressive nor hawkish enough on key foreign policy issues.

"It's difficult to make the case that someone who doesn't even see the merits of the fall of Bashar al-Assad for American interests deserves to have the top Republican spot on the committee," said one GOP foreign policy pundit. "There are other Republicans, such as Sen. Rubio, who have advocated a much more coherent and thoughtful foreign policy vision that might make them more appealing replacements for Sen. Lugar."