Sen. Jim DeMint (R-S.C.) might back primary challengers to incumbent Republican senators after all.

DeMint had promised after last year's election that he would not endorse any opponents to his fellow Republican senators. But now he is angry enough with the debt-ceiling compromise that Senate Minority Leader Mitch McConnellAddison (Mitch) Mitchell McConnell32 male senators back Senate women's calls to change harassment rules Duckworth brings her baby to Senate vote, drawing a crowd FreedomWorks backs Jim Jordan for House Speaker MORE (R-Ky.) and House Speaker John BoehnerJohn Andrew BoehnerSome doubt McCarthy or Scalise will ever lead House GOP Lobbying World McCarthy courts conservatives in Speaker's bid MORE (R-Ohio) struck with President Obama that he may back serious challengers to Republican senators who support the plan, according to a source close to the senator.

ADVERTISEMENT
"He's already opened the door to changing that policy in terms of supporting people in primaries — this deal could bring him to the point where he says he's not going to make any guarantees," said the source, who asked not to be identified because of the sensitive nature of intraparty relations. "It's not a threat that he's going to oppose anybody, but ... if he does, nobody should be surprised."

DeMint, whose Senate Conservatives Fund helped finance several conservative Republican candidates last election, angered Republican leaders when he backed a handful of conservative challengers to candidates backed by the establishment.

He supported Sen. Rand PaulRandal (Rand) Howard PaulHeitkamp becomes first Dem to back Pompeo for secretary of State Senate committee sets Monday vote even as Pompeo appears to lack support Trump checkmates Democrats in sending Pompeo to North Korea MORE (R-Ky.) over McConnell's favored candidate in Kentucky and helped give Sen. Marco RubioMarco Antonio RubioSenate confirms Trump’s pick to lead NASA The Hill's 12:30 Report Steps Congress can take to defend America against foreign influence operations MORE (R-Fla.) an early boost in his primary against former Florida Gov. Charlie Crist (I).

After the 2010 elections, DeMint promised his colleagues he would not endorse any primary candidates, but the debate over raising the debt ceiling has changed his mind. DeMint said in mid-June that "if we have folks who go the wrong way on [the debt ceiling vote], it's going to be pretty hard for me to sit still" and stay out of primaries. 

The new deal does not pass muster with him, which should worry some of his fellow senators. The Senate Conservatives Fund spent $8.2 million on its preferred candidates last election cycle, and DeMint has said he hopes to raise and spend $15 million this time around.

He has already endorsed two Republicans in possibly competitive Senate primaries this year: Ohio Treasurer Josh Mandel and former Texas Solicitor General Ted CruzRafael (Ted) Edward Cruz32 male senators back Senate women's calls to change harassment rules Senate confirms Trump’s pick to lead NASA DOJ denies reports judicial nominee once called illegal immigrants 'maggots' MORE.

Republican senators who may face competitive primary challenges from the right include Sens. Dick Lugar (Ind.) and Orrin HatchOrrin Grant HatchGOP senators raise concerns about babies on Senate floor House passes series of bills to improve IRS Senators, staffers lament the end of 50 Most Beautiful MORE (Utah). Other incumbents, including Sens. Olympia Snowe (Maine) and Bob CorkerRobert (Bob) Phillips CorkerTrump backs Blackburn's Tennessee Senate bid Senate committee sets Monday vote even as Pompeo appears to lack support Corker has 'no idea' if Trump will run for reelection MORE (Tenn.) have angered conservatives at times, but a credible candidate has not emerged to challenge either of them.