Texas Rep. Pete Sessions, in a statement late Thursday, said he had decided to abandon the race after it "became obvious to me that the measures necessary to run a successful campaign would have created unnecessary and painful division within our party."
Sessions, who serves as chairman of the House Rules Committee, has no plans to seek the No. 3 job of whip, said his spokeswoman, Torrie Miller. Three others are seeking that post.
Within 48 hours of Rep. Eric Cantor's lightning primary-election downfall, McCarthy and his deputies aggressively rounded up votes with a pitch to Southern Republicans and pointed private conversations on the House floor in a race that occasionally had the markings of a personality-driven contest for class president.
Republicans sought to project an aura of unity but failed to quiet conservative complaints that such quick party elections after Cantor's defeat gave them little time to rally around an alternative who better reflects the right's ideology and the emboldened tea party.
The votes next Thursday for majority leader and whip may well not be the end of it. Several Republicans asserted that next week's action won't quiet ambitious lawmakers or factions in the GOP caucus, and leadership contests after November's national midterm elections could produce a brand new lineup.
Despite conservative discontent, Boehner's job does not appear to be in serious jeopardy. But some lawmakers noted there was a limit to his security.
"The speaker is speaker in 24-hour increments. Literally 50 guys can call a revolt," said Rep. Tom Cole of Oklahoma, a Boehner ally.
Cantor suffered a stunning defeat to little-known college professor Dave Brat in Tuesday's Virginia Republican primary, a race that underscored the rift within the GOP between pragmatic, establishment conservatives and farther-right contenders pressing for no-compromise ideological stances. Brat cast Cantor's past positive comments on possible immigration changes as amnesty for those here illegally - a characterization Cantor heatedly rejected - and turned it into a defining issue in the race.
Cantor is the first House majority leader to lose his seat by being defeated in a party primary election since the post was created in 1899, according to Eric Ostermeier, research associate at the University of Minnesota's Center for the Study of Politics and Governance.
Cantor announced on Wednesday that he would step down as majority leader at the end of July. He endorsed McCarthy as his successor, and the House whip moved swiftly to secure the votes.
"I don't think anyone counts votes better around here, and I think he has a very, very commanding lead," Cole said.
Another Texan with stronger bona fides in the conservative ranks, Rep. Jeb Hensarling, passed on the race on Thursday, saying, "After prayerful reflection, I have come to the conclusion that this is not the right office at the right time for me and my family."
If conservatives were powerless to put the brakes on McCarthy's quick rise they weren't keeping quiet about their frustration.
Rep. Steve King, R-Iowa, was among several lawmakers calling on GOP leaders to put off the election, suggesting it was rigged.
"Leadership's tactic has always been call the election as fast as you can, don't let anybody have time to organize except those who had the heads-up and the head start," King said.
Hensarling had been the conservatives' choice, and King and others had no one else to get behind.
"I'm looking for a candidate that has not supported some form of amnesty, and Jeb fit that, and now we don't have an announced candidate that fits that and I'm very troubled by that," King said. "Because if there's any single issue that cost Eric Cantor his seat, it was amnesty."
The discontent seemed to irritate some of McCarthy's supporters who mocked criticism that their candidate wasn't conservative enough.
"When they say 'More conservative this, more conservative that,' it doesn't mean anything to me. The more exotic members around here once again failed to have a candidate, they failed to show up. They don't debate. So they don't like any of the candidates," said Rep. Devin Nunes, R-Calif., who was lining up votes for McCarthy.
"They just come out here to you guys and complain, and they blog and they Facebook, but when it's time to actually raise money and go recruit candidates and win elections so that you can stop Obama which is what they say they want to do, they don't have the capability of doing it," Nunes said.
Rep. Charles Boustany, R-La., said some conservatives are "never satisfied."
While the majority leader race narrowed to a single candidate, the contest to replace McCarthy as whip expanded with the addition of Rep. Marlin Stutzman of Indiana.
Already seeking the post were Reps. Peter Roskam of Illinois, who has been chief deputy whip, and Rep. Steve Scalise of Louisiana. He is head of the Republican Study Committee, the organization representing conservative GOP lawmakers.
Currently all four top GOP leaders are from states President Barack Obama carried in 2012: Ohio, Virginia, California and Washington state. Several Republicans have argued that members of the GOP leadership should be limited to lawmakers from deep red states that voted for the GOP in recent presidential elections.
"I think that's a silly argument," said Rep. Adam Kinzinger of Illinois, who argued that in the House "we don't elect people by state, we elect them by districts."
Boehner, asked whether he would endorse McCarthy, sidestepped the question, saying, "I can work with whoever gets elected."
In a closed-door GOP caucus on Wednesday, Boehner stressed the importance of unity ahead of midterm elections when the GOP is expected to increase its majority in the House and possibly win control of the Senate.
After the national elections, another round of contests for party leaders will occur, and Republicans could field a new slate of candidates.