“No one can bat a thousand,” he said. “And while a few candidates from outside the mainstream have emerged that will have challenges winning a general election, the playing field is more than wide enough to recapture a majority.”

In a few cases, the candidate whom Mr. McCarthy failed to defeat is thriving, and the outcome of the primary might not affect Republicans’ chances in the general election. Recent public polls have shown Mr. Williams, for instance, ahead of Francis Conole, the Democrat competing for an open seat in a competitive district in upstate New York.

Mr. McCarthy’s super PAC often spends in places where its favored candidate is struggling, so it is not surprising that even with the outside boost of funds, some of those candidates still lost. Overall, the Congressional Leadership Fund sees its primary spending as a success story. The group helped several Republican incumbents fend off challenges from more extreme candidates in competitive districts, including Representatives Brian Fitzpatrick in Pennsylvania, David Valadao and Young Kim in California and Andrew Garbarino in New York.

“By recruiting strong candidates and supporting them through their primaries, we were able to make our own luck,” said Dan Conston, the organization’s president. “Candidate quality matters, and proactively engaging put us in a dramatically better position not to just win the majority, but to elect stars that will be the future of the party.”

But elsewhere across the country, right-wing candidates whom Mr. McCarthy tried to knock out have prevailed, bolstering Democrats’ chances of winning a seat.

In Arizona, Kelly Cooper, who has refused to acknowledge the 2020 election results and called for the immediate release of people who stormed the Capitol on Jan. 6, defeated Tanya Wheeless, the granddaughter of a Mexican immigrant whom Mr. McCarthy’s PAC endorsed and helped fund.

In the Third Congressional District in Washington, a group aligned with Mr. McCarthy, Take Back the House 2022, donated to Representative Jaime Herrera Beutler, who was one of 10 Republicans who voted to impeach Mr. Trump. But she was defeated in her primary by Joe Kent, who has said he would oppose Mr. McCarthy for the speakership if elected.