Several Republican senators up for reelection in 2012 are being threatened with primary challenges because of their support for the new START Treaty.

At least one group, the National Republican Trust PAC, has vowed to make the START Treaty its No. 1 2012 issue. 

{mosads}As The Hill’s Alexander Bolton reports, Senate Democrats are confident they have the votes of at least nine Republican senators — the number they need to get the treaty passed in the Senate. That vote could happen as early as Tuesday.  

Among those nine are likely to be four Republicans who face reelection in 2012 — a handful who are already in the electoral crosshairs of Tea Party activists.   

Sen. Scott Brown (R-Mass.) announced his support for the treaty on Monday. Brown, who is running for a full six-year term in 2012, has already been talked about as a Tea Party target, given his centrism on a handful of key Senate votes.  

Sen. Dick Lugar (R-Ind.), who has helped lead the charge for the treaty in the Senate, also faces a potential threat from the right because of his support of START, the DREAM Act and his vote in favor of the Troubled Asset Relief Program (TARP).  

Sen. Olympia Snowe (R-Maine) is also a vote to ratify the treaty. Even though Snowe has been tacking right and recently won the support of Maine’s new Tea Party-backed Gov. Paul LePage (R), she remains a likely primary target in ’12.   

Another likely yes vote on the GOP side is Sen. Bob Corker (R-Tenn.), who said Monday that he intends to vote in favor unless the Senate debate becomes “derailed” over the next two days.  

Corker told The Ballot Box last week that he hasn’t heard any noise back home about a Tea Party-backed primary challenge to him next cycle, claiming that his record on spending and deficits is in line with Tea Party activists.  

It’s far from clear whether START would be an issue of much potency in a GOP primary in 2012, particularly if the treaty passes with close to 70 votes in the Senate.

But the executive director of the National Republican Trust PAC last week penned a letter to National Republican Senatorial Committee Chairman John Cornyn (Texas) pledging to recruit primary challengers to GOP senators who vote in favor of it. 

Richard Grenell, who was a spokesman at the U.N. under then-President George W. Bush, has also called for primary challenges to GOP senators who back START. 

“Republican senators who vote to approve of President Obama’s weak negotiation strategies deserve to be challenged in a primary election and defend their inattentive national security votes,” Grenell recently wrote on the Huffington Post.

Several other Republicans who face reelection in 2012 are likely to be “no” votes on START, led by Sen. Jon Kyl (Ariz.). Sens. Kay Bailey Hutchison (Texas), Orrin Hatch (Utah), John Barrasso (Wyo.), Roger Wicker (Miss.) and John Ensign (Nev.) have also voiced opposition to the treaty.