Indiana Sen. Dick Lugar’s primary loss Tuesday symbolizes a changing of the guard not just for Republican politics, but for the party’s foreign policy. The GOP, however, has a rather thin bench of lawmakers ready to succeed their longtime standard-bearer on the Foreign Relations Committee.

Next in line after Lugar on the Republican side of the committee is Tennessee Sen. Bob Corker, whom observers on and off the Hill expect to fill the post barring an unanticipated challenge or an opportunity to take over the helm of the Banking Committee.

“The default position,” one Republican aide said, “is that Corker takes over.”

Most of the rest of the Republicans currently on the committee have put a priority on policy interests closer to home and thus have their eyes on possible opportunities in committees other than Foreign Relations. For Sen. James Risch (Idaho), that means looking to move up the ladder at the Small Business and Entrepreneurship Committee when ranking member Olympia Snowe (R-Maine) retires. Sen. John Barrasso (Wyo.), meanwhile, has carved out a niche as a senior member of both the Energy and Natural Resources and the Environment and Public Works committees.

The only other GOP member of the committee likely to be at all interested in the top slot on Foreign Relations is Sen. Marco Rubio (Fla.), who has made foreign affairs a key part of his policy agenda since joining the Senate last year. And unlike many other Republicans, who spend a few years on Foreign Relations before moving to more powerful committees such as Appropriations or Finance, Rubio has said he wants to remain on the committee for the long term. Rubio, who has national ambitions, is widely seen as trying to use the panel to burnish his diplomatic credentials, much as President Barack Obama tried to do during his years in the Senate.

The relative inexperience of Corker and Rubio — Corker is in the sixth year of his first term, Rubio in the second year — stands in stark contrast to Lugar’s decades of foreign policy experience. The six-term Senator, a senior member of the Foreign Relations Committee since the mid-1980s, earned a reputation as a foreign affairs wonk thanks to his role in some of the country’s most pivotal policies at the end of the Cold War. But his sway within the chamber and his own party has ebbed during the past decade.

Those trends speak to the broader marginalization of the Foreign Relations Committee in the Senate, particularly among Republicans. The GOP caucus continues to rank the panel, along with the Armed Services, Appropriations and Finance committees, as a “Super A” committee. Senate Republicans are allowed to serve on only one Super A committee at a time, unless they obtain a waiver from the party.

But while Armed Services, Appropriations and Finance all continue to maintain their cachet among lawmakers — largely because they offer ample opportunity to promote parochial interests — Foreign Relations is no longer regarded as such a plum post. While it used to pass regular State Department authorization bills, that practice screeched to a halt during the 1990s. Its main sources of clout now stem from authorizing treaties and confirming nominations.

It’s one of the reasons the committee now draws few GOP Senators with any intention of staying on for the long term and developing expertise on the issues before the panel.

Lugar himself has lamented the “considerable” turnover on the committee in recent years. In an interview last fall, he said he has tried to encourage new Members to stay on the committee, “and, in fact, some have rather loyally stayed with it.”

“But then, finally, they feel because of constituent interests that they need to move elsewhere,” he said.

Most leading Republican voices on foreign policy in the Senate now come from outside the committee — John McCain (Ariz.), ranking member of Armed Services; Lindsey Graham (S.C.), ranking member of the Appropriations subcommittee that funds the State Department; and Mark Kirk (Ill.), who has emerged as a key player on Iran sanctions and broader Middle East policy.

That pattern is bound to continue, regardless of who is at the helm of Foreign Relations.