When Liz Cheney announced this week that she would challenge Wyoming Sen. Mike Enzi in a Republican primary next year, the national party coalesced swiftly and unequivocally behind Enzi.

“The primary responsibility of the Senate campaign committee is to make certain that Republican incumbents are re-elected,” Sen. Jerry Moran, R-Kan., head of the National Republican Senatorial Committee, said after Cheney’s announcement. “We’ll do everything we can to make certain that Mike Enzi has the help and support he needs from us.”

On the House side, however, there is no such institutional obligation to protect incumbents financially.

For House Agriculture Committee Chairman Frank Lucas, R-Okla., that hands-off policy could have deeply personal repercussions: Lucas is one of 10 House Republicans being targeted by the powerful conservative group Club For Growth, which hopes to replace moderate GOP members of Congress with more conservative candidates.

The NRCC won’t spend money to counter the influence of the Club and other outside groups in safe GOP districts — a policy that makes sense, Lucas said, because Republicans have limited money for the election cycle. Besides, he said, the party should not need to force its favored candidates on voters.

“But, by the same token, we do have so many outside groups playing in primaries that you have to wonder about the nature of that policy,” Lucas said.

Primary challenges to incumbents are not unique to House Republicans, but outside liberal groups have tended not to target Democratic incumbents to the extent conservatives do.

The magnitude and visibility of the trend within the Republican Party drove former Rep. Steve LaTourette to declare this week that the outside group he leads, Main Street Advocacy, will use its super PAC to offset Club for Growth’s influence in 2014.

“The days of the Club for Growth using their special interest money to bigfoot Republican primaries and bully members of Congress is over,” LaTourette, R-Ohio, said in a statement. “We will fight them dollar for dollar.”

The Club had no response to LaTourette’s comment.

And the NRCC stands by its policy, rationalizing that money is best spent in the districts will it where make the biggest difference on Republican control of the House.

“We are focused on beating Democrats,” said NRCC spokesman Daniel Scarpinato. “Our goal is to protect and strengthen the majority.”

“We’re focused on the races that will decide the control of the House of Representatives,” Scarpinato added.

By design, the Club for Growth does not target races in competitive districts for Republicans. Instead, it focuses on changing GOP representation in the House by training its considerable resources on safe GOP districts with open seats or those occupied by incumbents who aren’t well-aligned with the group’s positions.

“One of the things that makes us different is that we’re one of the only groups willing to get involved in a Republican primary,” said Club spokesman Barney Keller.

In 2012, the Club played a role in Republican Richard Mourdock’s primary victory over then-Sen. Richard Lugar, of Indiana, but it did not help unseat a sitting Republican House member.

That statistic is small comfort to Rep. Adam Kinzinger, R-Ill., another Club target in 2014. Still, Kinzinger doesn’t think the NRCC’s policy is unreasonable.

“I understand where they’re coming from,” Kinzinger said. “And it’s a leadership decision.”

Kinzinger, like Lucas, also in concerned about the growing influence of well-funded outside groups on primary elections.

“But the days of that might be coming to an end,” Kinzinger said. “I think people are tired of Washington interests deciding elections.”

Correction: An earlier version of this post stated that the NRCC does not endorse candidates in GOP primaries in which one candidate is an incumbent. The committee does, in fact, endorse incumbents in those races.