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 McConnellMitch McConnellFive fights for Trump’s first year Warren builds her brand with 2020 down the road AACR’s march on Washington MORE (R-Ky.) and House Speaker John BoehnerJohn BoehnerLobbyists bounce back under Trump Business groups silent on Trump's Ex-Im nominee Chaffetz won't run for reelection 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.

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"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 PaulRand PaulWe can put America first by preventing public health disasters Conservative activists want action from Trump McConnell: 'Big challenge' to pass ObamaCare repeal in Senate MORE (R-Ky.) over McConnell's favored candidate in Kentucky and helped give Sen. Marco RubioMarco RubioTop Trump officials push border wall as government shutdown looms Rubio defends Trump: 'This whole flip-flop thing is a political thing' Rubio: Shutdown would have 'catastrophic impact' on global affairs 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 CruzTed CruzWarren builds her brand with 2020 down the road Trump wall faces skepticism on border No Congress members along Mexico border support funding Trump's wall MORE.

Republican senators who may face competitive primary challenges from the right include Sens. Dick Lugar (Ind.) and Orrin HatchOrrin HatchChaffetz's campaign arm registers 2028 websites The Hill's 12:30 Report Chaffetz won't run for reelection MORE (Utah). Other incumbents, including Sens. Olympia Snowe (Maine) and Bob CorkerBob CorkerGroups warn of rural health 'crisis' under ObamaCare repeal Ringing the alarm in Congress: 20 million lives at risk due to famine Senators want more efficient way to get food aid to Africa MORE (Tenn.) have angered conservatives at times, but a credible candidate has not emerged to challenge either of them.