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 McConnellSessions: 'We should be like Canada' in how we take in immigrants NSA spying program overcomes key Senate hurdle Overnight Finance: Lawmakers see shutdown odds rising | Trump calls for looser rules for bank loans | Consumer bureau moves to revise payday lending rule | Trump warns China on trade deficit MORE (R-Ky.) and House Speaker John BoehnerJohn Andrew BoehnerDems face hard choice for State of the Union response Even some conservatives seem open to return to earmarks Overnight Finance: Trump, lawmakers take key step to immigration deal | Trump urges Congress to bring back earmarks | Tax law poised to create windfall for states | Trump to attend Davos | Dimon walks back bitcoin criticism 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 PaulRandal (Rand) Howard PaulNSA spying program overcomes key Senate hurdle Fix what we’ve got and make Medicare right this year Despite amnesty, DACA bill favors American wage-earners MORE (R-Ky.) over McConnell's favored candidate in Kentucky and helped give Sen. Marco RubioMarco Antonio RubioOvernight Cybersecurity: Bipartisan bill aims to deter election interference | Russian hackers target Senate | House Intel panel subpoenas Bannon | DHS giving 'active defense' cyber tools to private sector Senators unveil bipartisan push to deter future election interference Puerto Rico's children need recovery funds 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 CruzWith religious liberty memo, Trump made America free to be faithful again Interstate compacts aren't the right way to fix occupational licensing laws Texas Dem: ‘I don’t know what to believe’ about what Trump wants for wall MORE.

Republican senators who may face competitive primary challenges from the right include Sens. Dick Lugar (Ind.) and Orrin HatchOrrin Grant HatchKoch groups: Don't renew expired tax breaks in government funding bill Hatch tweets link to 'invisible' glasses after getting spotted removing pair that wasn't there DHS giving ‘active defense’ cyber tools to private sector, secretary says MORE (Utah). Other incumbents, including Sens. Olympia Snowe (Maine) and Bob CorkerRobert (Bob) Phillips CorkerSenate campaign fundraising reports roll in Congress should take the lead on reworking a successful Iran deal North Korea tensions ease ahead of Winter Olympics MORE (Tenn.) have angered conservatives at times, but a credible candidate has not emerged to challenge either of them.