Updated: 5:30 p.m.

In the waning days of a bruising primary between Illinois GOP Reps. Adam Kinzinger and Don Manzullo, House Majority Leader Eric Cantor donated $25,000 to an anti-incumbent super PAC for use against Manzullo — a move that may have helped swing the contest in favor of Kinzinger.

The Virginia Republican had previously endorsed Kinzinger and donated directly to his campaign, which was unusual in and of itself and which drew the ire of Manzullo and some older members of the GOP Conference.

Cantor has previously defended his backing of Kinzinger, arguing that he had promised to support him before the freshman decided to run in the same district as Manzullo. Cantor’s overt backing of Kinzinger did not directly target Manzullo, but YG Action Fund, a super PAC run by a former Cantor aide, spent $52,000 on a radio ad buy supporting Kinzinger.

But Cantor’s decision to donate significant resources to the Campaign for Primary Accountability, which targets House Republican and Democratic incumbents across the country and ran ads harshly critical of Manzullo, is sure to reignite the controversy.

Cantor campaign spokesman Ray Allen told Roll Call that Cantor made the donation at the request of Rep. Aaron Schock (R-Ill.) for use only in the Kinzinger-Manzullo race.

“On Thursday, March 15, 2012, Leader Cantor was asked by Congressman Schock to contribute to an organization that was supporting Adam Kinzinger in the Illinois election of March 20. ERICPAC subsequently made a contribution with the understanding that those funds would be used only in the effort to support Congressman Kinzinger,” Allen said.

Allen also made it clear that Cantor’s involvement in the Illinois primary was a one-time decision and that he does not support the CPA’s effort to oust incumbent Members.

“Leader Cantor does not support the actions of this organization in any other election,” Allen said.

In an interview, Schock explained that with polls showing Kinzinger and Manzullo locked in a tight race, he decided to approach the CPA about helping expand an ongoing advertising campaign that they were running against Manzullo.

“The final week of the campaign, it got very tight, it was neck and neck. I was trying to do everything I could to help the Kinzinger campaign and reached out to the committee that was running ads in support of them,” Schock said.

“They were basically running the television ads for him, [and] I asked if I could specify a donation to them” to be used only the Illinois primary.

“And they said I could,” Schock said, adding that he discussed the legality of the arrangement with the National Republican Congressional Committee.

However, a Schock spokesman later clarified and said the Congressman misspoke and that the donations were not vetted with the NRCC but with attorneys specializing in Federal Election Commission law.

Convinced he was on sound legal footing, Schock approached Cantor.

“I said, ‘Look, I’m going to do $25,000 [specifically] for the Kinzinger campaign for the television campaign’ and said, ‘Can you match that?’”

“And he said, ‘Absolutely.’”

Schock made his donation through his GOP Generation Y Fund leadership PAC.

In a statement released to Roll Call, the CPA did not comment directly on the donations from the two lawmakers, but it said that, “The Campaign for Primary Accountability is committed to providing resources to help voters make informed decisions in elections involving long-term entrenched incumbents in the U.S. House of Representatives. … We welcome the support of anyone who shares our goals regardless of political persuasion, whether they are from the grassroots or from the leadership of the Democratic or Republican parties.”

Cantor’s donation to the CPA came during the same weekend that Manzullo was ripping into the Majority Leader, telling national and local media that Cantor’s decision to endorse Kinzinger had created a massive rift within the Conference and calling on him to step down as Majority Leader. Kinzinger’s decision to challenge Manzullo in the newly drawn 16th district came after state Democrats drew him into a heavily Democratic district. Kinzinger moved into the 16th, which includes parts of both his and Manzullo’s former districts.

Although Cantor’s endorsement of Kinzinger does not appear to have had the dire consequences Manzullo and others had predicted, the Republican leader is nevertheless sensitive to his Members’ concerns, sources close to Cantor said.

Cantor “is reaching out to Members. … It’s safe to say he’s had conversations with Members since he endorsed Kinzinger,” one Republican source said.

Schock acknowledged the donations will likely “raise some people’s eyebrows … [but because] you can actually earmark the money, that will hopefully satisfy some people’s concerns.”

He also defended his and Cantor’s decision to throw their financial weight behind Kinzinger, despite the difficult nature of a Member-vs.-Member primary.

“Leadership isn’t about doing what’s easy. … At the end of the day, when you want somebody to have your back, when you’re going to want their support, is when you’re in a gun fight, so to speak,” Schock said. “I like to get involved when I can make a difference.”

Still, that may be cold comfort to more than a dozen Republicans facing challenges from the CPA.

In addition to Manzullo, the organization has opposed several Members who have already had primaries, including Financial Services Chairman Spencer Bachus (R-Ala.) and Reps. Jesse Jackson Jr. (D-Ill.) and Jean Schmidt (R-Ohio). Although Bachus and Jackson survived their primary fights, Schmidt did not.

Other GOP Members either already being targeted by the CPA or under consideration include Pennsylvania’s Tim Murphy; North Carolina’s Walter Jones Jr. and Howard Coble; Texas’ Ralph Hall, Joe Barton, John Culberson, Kevin Brady, Mike Conaway, Lamar Smith and Kenny Marchant; and California’s Dan Lungren, Gary Miller, John Campbell and Brian Bilbray, among others.

The CPA spent a whopping $222,000 on Kinzinger’s behalf late in the race. The six-figure sum is more cash than the controversial, Texas-based super PAC has spent in any other race this cycle.

The super PAC spent at least $75,000 on television ads and $18,000 on radio spots knocking Manzullo and pumping Kinzinger, according to FEC records. Online reports show it also unloaded at least $104,700 in direct mail on the race through postcards and other pieces.

Manzullo lost the primary to Kinzinger by 12 points.

Shira Toeplitz contributed to this report.