Sen. John Thune (R-S.D.) did the unthinkable in 2004 when he defeated then-Minority Leader Tom Daschle, but that achievement has yet to propel him into a leadership post — until now.

Thune, 47, has quietly been preparing a run for the Republican Conference vice chairmanship in the 111th Congress. Although the post is the most junior in the GOP hierarchy, it’s viewed as a stepping-stone for any Senator seeking to ascend in the leadership ranks.

Although Thune has publicly refused to say whether he’s mounting a bid, sources close to the South Dakota Republican say he has been making calls to take the temperature of his colleagues and to shore up commitments for a prospective bid. Leadership elections will take place the week of Nov. 17 when Congress returns for a brief, lame-duck session.

One GOP source said once tomorrow’s elections are over, Thune “will pull the trigger fast” in launching his internecine campaign for the vice chairmanship. Sen. John Cornyn (Texas) is the current vice chair, but plans to vacate the job to run for chairman of the National Republican Senatorial Committee next year.

Kyle Downey, Thune’s spokesman, declined to telegraph his boss’ plans before Nov. 4, but wouldn’t discount a leadership bid. Thune currently holds an unelected leadership job as the Chief Deputy Minority Whip, under Minority Whip Jon Kyl (Ariz.).

“Sen. Thune is busy working to re-elect his Senate colleagues, but will address opportunities to further serve the party after Tuesday’s election,” Downey said.

Thune has entertained entering the leadership before. He considered running for NRSC chairmanship in 2006, but ultimately opted out, citing the travel and family obligations.

Thune’s future isn’t the only one in play. Senate Republicans are poised to consider openings to at least three posts — the chairmanships of the Republican Policy Committee and the NRSC, in addition to vice-chairmanship of the Conference.

Cornyn and Sen. Norm Coleman (Minn.), who is locked in a tight re-election battle, are the leading candidates for the NRSC, while the current campaign committee chairman, Sen. John Ensign (Nev.), is running unopposed for the policy gavel. Ensign would take over for Sen. Kay Bailey Hutchison (R-Texas), who has decided not to seek the post again. Hutchison is exploring a gubernatorial bid in her home state.

Thune appears to be the leading candidate for the vice chairmanship, although it is possible other up-and-coming Senators could jump in the race. Sens. Richard Burr (R-N.C.), who unsuccessfully sought conference chairmanship a year ago, Lisa Murkowski (Alaska) and Jeff Sessions (Ala.) also have been mentioned as possible contenders.

Although Senate Republicans are expecting just three vacancies in their ranks, more positions could become available if Nov. 4 brings across-the-board devastation.

Minority Leader Mitch McConnell (R-Ky.), who is seeking a fifth term, has been fending off a tough challenge from Democratic upstart Bruce Lunsford. McConnell is expected to survive, but his ousting would mean a complete reshuffling of the leadership. Under that scenario, some have speculated that Thune would run to be the next Minority Whip, assuming Kyl climbs into the Minority Leader job. The Conference Chairman, Lamar Alexander (Tenn.), also would be a top contender for the No. 2 whip slot.

Thune seems well positioned to enter the leadership next year, but he isn’t without detractors. The junior GOP lawmaker irked some of his colleagues earlier this year by joining a bipartisan group, known as the “Gang of 10,” which sought to tackle the summer’s high gasoline prices. Some in the Conference felt the Republican lawmakers involved were hurting the party’s efforts to make gasoline prices a successful election-year issue.

One former Republican leadership aide, however, said Thune recognized his participation in the group could undermine his future ambitions, saying: “He was in the ‘Gang of 10.’ That was not very helpful. But, he bowed out gracefully. That could have hurt him.”

Still others say Thune has been doing what’s necessary to prove his worth in the Conference, and make the case for a future in leadership. A senior Republican staffer said Thune has taken the time to study the Senate and develop relationships, while also being careful not to “veer too far from where the state is.”

“He is a solid member. He’s got a future. One needs to be here for a while before you realize the full potential,” said the Republican aide.