The Ohio Republican, who has served as the Speaker of the House since 2011, told colleagues in a closed-door gathering Friday morning that he would leave at the end of October, sending shockwaves through the chamber.
Ohio GOP Rep. Steve Chabot, who described the mood in the room as "somber" and said there had been tears from Boehner, said the subject of who would replace the Speaker had not come up. But he predicted that this would begin in "five minutes."
If McCarthy wins the gavel, it would mark the continuation of an incredible ascent for the California Republican, who has only held the second highest ranking job in the House since last summer. McCarthy himself was only said to have found out about Boehner's resignation moments before Friday's morning meeting.
During his press conference Friday afternoon, Boehner effectively endorsed McCarthy. "I am not going to be here to vote on the next Speaker. But that's up to the next members. But having said that, I think that Kevin McCarthy would make an excellent Speaker," Boehner said.
Two sources familiar with McCarthy's lobbying efforts told CNN Friday night that they feel he's in a good place to get the votes to become Speaker. He spent the whole day talking to people and will continue to talk to every single member of the GOP conference, the sources said.
Although he's part of the "establishment" leadership, he has good relationships with many of the newer members, many of whom he helped recruit.
One of the sources said there's going to be an effort to make sure House Republicans have a good understanding of who McCarthy is and where he came from, defining him before others can do it for him. The source cited accusations that he is pro-amnesty on immigration as an area in particular that they want to defend him over.
But McCarthy is expected to face a challenge for the speakership, though it's unclear how serious that fight will be. The chamber's conservative faction may instead choose to focus on winning another post -- such as majority leader or whip -- instead.
Among the lawmakers who could seek the majority leader spot are Reps. Steve Scalise of Louisiana (the current Whip), Cathy McMorris Rodgers of Washington state and Tom Price of Georgia.
Deputy Whip Patrick McHenry, R-North Carolina, is a leading candidate to be the next whip, and Rep. Markwayne Mullin of Oklahoma has also indicated he will seek the role.
Scalise held a conference call Friday night with his whip team to tell the House vote counters that he will run for majority leader if McCarthy were to become speaker, according to a source with knowledge of the call. As majority leader, Scalise said he would work with every Republican to advance conservative legislation, and said he would ensure the House took the steps to develop consensus within the caucus.
Scalise added that Boehner's decision to resign was "one of the most selfless things I've ever seen."
On Saturday, Rep. Peter Roskam, R-Illinois, called for a special conference meeting head of the vote for the next Speaker.
"Healing our divisions and uniting behind the conservative policy solutions the American people deserve will help our members and it will empower the new leaders we select," he said in a letter to colleagues.
Roskam said he was not announcing a run for any leadership position, but several House Republicans said he is making calls and positioning to join the race for majority leader.
Opportunity for tea party conservatives
Boehner's exit also creates an opening for the more conservative wing of the House caucus. Boehner has long faced intense pressure from his conservative colleagues to take more of an ideologically purist stance on divisive issues like Obamacare and the Export-Import Bank.
In October 2013, the government entered into a partial shutdown when lawmakers were deadlocked on funding the Affordable Care Act, exposing a deep divide within the GOP.
More recently, the issue of funding for Planned Parenthood
has raised the alarm about another possible government shutdown. Conservative Republicans have sought to tie provisions to defund the organization to a government funding bill, amid outrage over videos that allegedly show officials from the group discussing the sale of fetal tissue.
President Barack Obama addressed Boehner's resignation during a press conference with Chinese President Xi Jin Ping Friday afternoon.
Obama said Boehner was a leader who understood that in governance, "you don't get 100% of what you want" -- and called on the next speaker to not resort to shutting down the government when faced with significant differences in opinion.
When asked who will run for speaker, Rep. Tim Huelskamp, R-Kansas, said: "Everybody! But the establishment lost today."
Huelskamp said he and other Tea Party Republicans were jubilant at the news of Boehner's resignation and believes that hard-line conservatives, often splintered, would agree on a candidate together and not offer any early endorsements.
"He read the writing on the wall," Huelskamp said. "We need new leadership. Every time we go home we hear, 'Fire Boehner.' We need a new speaker who can stand up to the president."
Rep. Raul Labrador, a favorite of conservatives who ran unsuccessfully for majority leader in January, declined to say Friday if he would run for Speaker. Several members of the House Freedom Caucus have pointed to Labrador as a possible candidate for Speaker or Majority Leader. Rep. Mark Meadows, R-North Carolina., who offered a resolution this summer that would have stripped Boehner of the Speaker's gavel, told reporters Friday he would not run to succeed Boehner.
Rep. Paul Ryan, the chairman of the influential House Ways and Means Committee and the Mitt Romney's vice presidential running mate in 2012, also will not run for the Speaker post, according to an aide.
Boehner's resignation comes amid record-low public approval of Congress — and deep discontent with Boehner's leadership.
An overwhelming 72% of Republican primary voters said they are dissatisfied with the ability of Boeher and Republican Senate Leader Mitch McConnell to achieve their party's goals, according to a new NBC News/Wall Street Journal poll
. In that survey, 36% said they want Boehner and McConnell immediately removed from their leadership positions.
Challenges a new leader will face
Texas GOP Rep Bill Flores said whoever follows Boehner will likely deal with the same political dynamic -- fellow Republicans who will want to "take your head off."
Flores said many House GOP members were frustrated with Senate Republicans for not pushing a more conservative agenda and voting on House-passed bills. "In my view the Speaker fell on his sword for all of Congress," he said, "and I hope the Senate starts to get things done."
Rep Lynn Westmoreland, R-Georgia, a Boehner ally, suggested the top post was a thankless job, asking, "who would want to be Speaker?"
He said he backed McCarthy, but said he didn't think Boehner's successor would have a much different impact on dealing with the divisions inside the conference.
"I think that the natives are restless and they want to see something change. So how much change somebody can bring about we'll see," Westmoreland said.
Westmoreland said he's received multiple phone calls already from multiple candidates seeking the Majority Leader job, but hasn't heard of anyone officially challenging McCarthy for Speaker.
California GOP Rep Devin Nunes told reporters he thought the leadership race could mean some new rules for how House Republicans operate. "You just can't' continue to have a super ultra-minority continue to try and dictate what happens in the House of Representatives," he said.