Democrats are claiming a $500,000 donation Sen. Jim DeMint's (R-S.C.) re-election committee gave to the Club for Growth will come back to bite the GOP in November.

Team DeMint donated the sum in January, Federal Election Commission reports show, to the Club for Growth, a fiscally conservative group that has frequently challenged Republicans it considers insufficiently conservative.

The two-term senator, a GOP kingmaker and leading voice for the conservative wing of the party, has taken a lower profile in Republican primaries this cycle than he did two years ago, when he supported a number of Tea Party candidates who went on to lose in the general election. His presence in those primaries put him at odds with the GOP establishment, although some of DeMint's picks rode to victory in part thanks to his support, including Sens. Marco RubioMarco Antonio RubioCongress faces growing health care crisis in Puerto Rico The Hill's 12:30 Report Colbert mocks Trump for sipping water during speech on Asia trip MORE (R-Fla.) and Pat Toomey (R-Pa.).

This cycle he told Republicans he wouldn't support primary challengers that could knock his fellow GOP lawmakers.

But his donation to the Club for Growth, which has been less hesitant to wade into primaries, has caused some angst within the Republican Party because one of the club's top targets is Sen. Dick Lugar (R-Ind.), who faces a major primary challenge from state Treasurer Richard Mourdock (R).

Complicating matters for Republicans is the prospect that Democrats, who are fighting to keep control of the Senate, could face better prospects for picking up the Indiana seat if Mourdock is the GOP nominee.

“These bloody primaries fueled by the Club for Growth and Jim DeMint are helping Democrats strengthen our position in key races this cycle,” said Democratic Senatorial Campaign Committee spokesman Matt Canter.

Just as in 2010, Canter said, infighting is poised to put unelectable GOP candidates on ballots, and DeMint's donation gives Republicans another half million reasons to worry as they try to gain the four seats they need (if President Obama wins reelection) to take control of the upper chamber.

"That's wishful thinking on their part," said DeMint spokesman Matt Hoskins. "The money DeMint is raising and contributing to help elect Republicans is second to none."

Hoskins noted they can't control which races the Club spends the donation in, but points out that four conservative candidates DeMint supports overlap with candidates the Club for Growth is supporting.

He added that the purpose of the donations was to facilitate efforts to help those candidates: Ted CruzRafael (Ted) Edward CruzTexas Republicans slam White House over disaster relief request Dem rep: Trump disaster aid request is 'how you let America down again' Moore endorsements disappear from campaign website MORE in Texas, Don Stenberg in Nebraska, Josh Mandel in Ohio and Mark Neumann in Wisconsin.

But in two of those races — Nebraska and Wisconsin — there is some concern among Republicans that the DeMint-backed candidate wouldn't perform as well in the general election and could hand the seat to Democrats.

Club for Growth spokesman Barney Keller declined to comment on whether DeMint's contribution had been earmarked for the four races where he has endorsed. But he said Democrats would be the ones to lose out if the group's favored candidates win their primaries.

"Ask Joe Sestak or Jack Conway how successful Club for Growth-endorsed candidates were last cycle," Keller said, referring to the Democrats' defeated Pennsylvania Senate candidate and the Democrats' 2010 nominee in Kentucky, respectively. "Maybe former Sen. Russ Feingold [D-Wis.] can expound or remind the DSCC about the club's help for electing conservative Ron JohnsonRonald (Ron) Harold JohnsonAlabama election has GOP racing against the clock Tax bills speed up global tax race to the bottom Someone besides the president should have the nuclear codes MORE to the Senate."

— This story was posted at 2:12 p.m. and has been updated.