House Majority Leader Eric Cantor (R-Va.) speaks as Grover Norquist, right, president of Americans for Tax Reform, and U.S. Rep. Kevin Brady (R-Tex.) look on during a news conference April 12 at the U.S. Capitol in Washington, D.C. (Alex Wong/Getty Images)

House Republican leaders suffered a humiliating legislative setback Wednesday when a large faction of GOP lawmakers rebelled against a leadership proposal that had drawn the opposition of powerful outside activists.

The mutiny forced House Majority Leader Eric Cantor (Va.) to abruptly pull from the floor legislation to shore up a program that allows people with preexisting health conditions to buy into an insurance pool for high-risk patients before they are able to transition to coverage under President Obama’s health-care law.

The measure is part of Cantor’s effort to rebrand the GOP after defeats in the 2012 presidential and Senate elections, but it quickly found resistance among conservative activists.

The Club for Growth led a contingent of right-leaning groups that urged Republican lawmakers to oppose the bill, casting it as a costly boondoggle that would do nothing to dismantle the health-care law.

“Fiscal conservatives should be squarely focused on repealing Obamacare, not strengthening it by supporting the parts that are politically attractive,” Andy Roth, a vice president of Club for Growth, wrote to lawmakers last week. Heritage Action, the political arm of the the conservative Heritage Foundation, joined in the opposition.

No Democrats supported the bill as it was considered by the House Energy and Commerce Committee because the $3 billion tab would be covered by revoking funding from a different piece of the health-care law. That let GOP leaders know they needed to wrangle almost every vote from their side of the aisle to pass the measure. The failure was reminiscent of flops they have experienced since seizing the majority in 2011.

Cantor pulled the bill after trying to push his rank-and-file members to support it during a closed-door huddle on Wednesday. He argued that “helping the sick people” was a worthy conservative cause. “This is the right thing to do,” Cantor said. “We’re trying to find solutions here.”

Conservatives rebel

On numerous occasions during the last Congress, Speaker John A. Boehner (R-Ohio) has tried to muscle legislation through the House with just Republican votes, only to see a couple of dozen conservatives rebel, some fearful of retribution from outside groups that specialize in financing primary challenges in safe GOP districts.

Unlike those previous battles, this one measured the clout not of Boehner but of his lieutenants. Cantor, 49, and House Majority Whip Kevin McCarthy, 48, have often been described as tea party leaders in Congress, part of the younger GOP generation that recruited the rabble-rousing class of 2010 that thrust Republicans into the majority.

Increasingly, however, conservative activists have signaled uneasy relations with the younger leaders. In January, they opposed a relief bill for communities hit by Hurricane Sandy, which Cantor had pushed, and the resulting passage of the measure was a legislative victory but a political embarrassment.

Cantor and McCarthy (Calif.), who wrote the book “Young Guns” together, supported the bill, but only 49 Republicans voted yes, while 179 opposed the measure. It passed because 192 Democrats backed it. House Budget Committee Chairman Paul Ryan (R-Wis.), who co-authored the book, also voted no.

For several months, Cantor has pushed a “making life work” agenda focused less on slashing federal spending and more on kitchen-table issues. The items tend to get easy-to-grasp names, such as the Helping Sick Americans Now Act, which lawmakers were supposed to vote on Wednesday but didn’t.

“I hear about the debt and the deficit. I hear about the fights,” McCarthy said in an interview in his Capitol office Tuesday. “And if I’m sitting at home, or if I’m trying to make within my household different things work or go forward, I think, ‘How does it relate to me?’ ”

While Cantor has been crafting the softer agenda, McCarthy’s job has been to secure the votes for its passage, a whip operation that fellow Republicans have privately mocked.

For a few dozen core conservatives, cutting spending and eliminating the health-care law are such paramount goals that they tend to oppose any new spending or any health-related bill that would not repeal the 2010 law — no matter what Cantor and McCarthy say.

“You’re replacing one big-government program for another big-government program, and I don’t think that’s what the American people are asking us to do,” Rep. Raul Labrador (R-Idaho) said Wednesday at a forum held by the Heritage Foundation.

Reconsidered in May

Some GOP lawmakers and aides said that the health-care measure appeared too quickly, winning committee passage last week, and that there was insufficient time to build support for it. Senior advisers suggested that it would be brought up again in May.

But the defeat signaled again that, only when a large bloc of Democrats is also voting with them can Republican leaders truly guarantee a floor victory.

Without Democratic support, GOP leaders have only about 15 votes of their own to spare. Club for Growth and Heritage Action have shown an ability to hold sway over a few dozen Republicans, those from the strongest GOP-leaning districts who would have the most to fear if a well-financed conservative challenger appeared in a primary.

On April 9, leadership brought a bill to the floor to allow state and local governments to purchase battlefield sites from the Revolutionary War. A few hours before the vote Heritage Action opposed the measure and announced that it would “key vote” the roll call, putting it in its rolling score card measuring how conservative a lawmaker is. The group declared it “irresponsible” for any government to be purchasing more land in such tight budgetary times.

Cantor, McCarthy, the entire leadership team and every major committee chairman supported the bill, including Ryan. It received just 101 Republicans votes, as 122 GOP lawmakers opposed it.

The measure passed only because of universal Democratic support.

Ed O’Keefe contributed to this report.

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