Emboldened conservatives are seizing on McCarthy's recent stumbles, insisting that he continues to lack the 218 votes necessary to secure the speakership on the House floor, and word spread Friday that Rep. Jason Chaffetz of Utah might join the race.
McCarthy infuriated Republicans by suggesting the probe into the deadly 2012 Benghazi attack was political in nature, giving fodder to many conservatives already eager to insert new blood into the House leadership. Chaffetz may give them the formidable candidate conservatives have thus far lacked.
Still the heavy favorite, McCarthy faces a pivotal moment next week when he meets with several key conservative blocs, including the House Freedom Caucus and the Republican Study Committee, to convince them that he offers something different from departing Speaker John Boehner.
It will be a difficult sales job. After meeting with a small group of conservatives in the House Freedom Caucus on Thursday, it was clear many were skeptical that anything would change.
"I certainly don't think he has 218 votes in the conference," said Rep. Justin Amash, R-Michigan. "Right now, there isn't a lot of evidence that if you just shift people up from one position to the next that you're going to get the change you need in this conference."
Tuesday evening, McCarthy and Rep. Daniel Webster, R-Florida, the only other declared candidate for the speaker's gavel, have been invited to appear with other leadership contenders at a forum of groups including the Tea Party Caucus, House Freedom Caucus and the Conservative Opportunity Society.
Rep. Tim Huelskamp, R-Kansas, an organizer of Tuesday night's forum, on Friday extended an invitation to Chaffetz to come -- if he decided to declare his candidacy for Speaker.
"We must ensure that whoever is the next speaker will work with conservatives, not against us," Huelskamp said in a written statement on Friday to CNN.
The next test for McCarthy later next week will be when he has to win the support of a majority of House Republicans -- or 125 -- in order to be chosen by his colleagues as the next candidate for speaker. But that is a prelude to the vote on the House floor expected later this month, when he will need a majority of the full House -- or 218 votes -- to take the top job in the chamber.
That means that McCarthy can't lose more than 29 Republican votes in a chamber where 25 Republicans already voted in opposition to Boehner earlier this year. If he does lose more than 29 votes, it could give rise to another potential candidate and throw the GOP House into further disarray.
With little margin for error, McCarthy went on "Fox News" Thursday evening to walk back his Benghazi comments, saying he "did not intend to imply in any way that the work is political."
Still, McCarthy's comments from earlier this week -- where he boasted that Clinton's "numbers are dropping" because of the work of the Benghazi committee -- became fodder for Democrats, who said it showed the panel was simply designed as a political witch hunt to target the Democratic frontrunner's record as secretary of state. McCarthy's comments came up in the closed-door meeting Thursday with the House Freedom Caucus, attendees said.
Chaffetz, the fourth-term Utah Republican who chairs the Oversight and Government Reform Committee, went on CNN earlier this week to blast McCarthy, calling on him to apologize for his comments. In a subsequent interview with CNN Thursday, Chaffetz said he personally told McCarthy the same message.
"He just digested it," Chaffetz said of McCarthy. "I told him I think he should withdraw them and explain how wrong they were."
Yet Chaffetz added on Thursday that "I support" McCarthy for speaker. "I reiterated I'm very supportive of you," he said he told the House majority leader in a private phone call.
On Friday, GOP sources told CNN that Chaffetz appeared to be gauging support for a potential speaker run himself. Politico first reported that the conservative lawmaker was preparing for a run.
Officials close to McCarthy discounted the potential impact Chaffetz may have on the race, noting that the House majority leader already has private commitments from a vast majority of the conference. Chaffetz, who did not respond to calls and text messages seeking comment Friday, has taken positions on an online sales tax bill that could put off some hard-line conservatives.
Webster the only declared opponent
Thus far, Webster lacks widespread support among conservatives and is not considered much of a threat.
The Friday rumblings underscore the discontent among some on the right for selecting McCarthy as speaker. The 50-year-old House majority leader has promised a more inclusive style of leadership than his predecessors, but it's unclear how much different a McCarthy speakership would be from a Boehner speakership.
Rep. Jeff Duncan of South Carolina, the three-term Republican and member of the House Freedom Caucus, said that McCarthy lacks enough support on the House floor to become speaker right now.
"It's not a given he's going to win that," Duncan said. "You gotta have 218."
Rep. Thomas Massie of Kentucky, who backs Webster, said the Benghazi comments should give conservatives a rallying cry against McCarthy.
"What Kevin said sounds like something you would hear in a smoke-filled back room on 'House of Cards.' It's not appropriate in Congress," Massie said on CNN Thursday.