Replacing House Speaker John Boehner could bring to the fore the ideological struggles between the GOP establishment and the vocal tea party insurgency.
The victor will signal which wing controls the House GOP. In either case, the role is a job opening with difficult — if not impossible — requirements. Boehner had been under prolonged pressure from conservatives in his party, who have accused him of failing to fight the Obama administration on issues important to the GOP.
"This is going to be a monumental fight within the caucus," said Nathan Gonzales, an analyst at the nonpartisan Rothenberg & Gonzales Political Report. "It will crystallize the infighting that has been going on for several cycles now between the establishment and the tea party wing."
Potential candidates to replace Boehner, who will resign as Speaker and leave his seat at the end of October, include House Majority Leader Kevin McCarthy of California, who served as Whip. McCarthy, Boehner's second in command, was informed of the Speaker's decision only shortly before he announced it to members of Congress in a closed-door meeting.
Another possibility is Texas Republican Jeb Hensarling, who serves as chairman of the House Financial Services committee and headed the conservative Republican Study Committee.
Former 2012 vice presidential candidate and Ways and Means committee chairman Paul Ryan said Friday that he's not going to run for the position.
"I'm not, it's a good job for an empty nester," said Ryan who has three school-aged children.
McCarthy is generally considered more of an establishment figure who has made some inroads with conservatives. Hensarling is generally well regarded by many members of the tea party.
"If one of these other people more tied to the tea party becomes part of leadership it would say clearly the tea party is on top," said Julian Zelizer, a professor of history and public affairs at Princeton University. "The tea party would reach a climactic moment and everyone will have to deal with an even more rambunctious GOP wing where 'no means no'."
Related: House Speaker John Boehner To Resign
In McCarthy, Republicans would get a House Speaker who has quickly worked his way up through leadership ranks. As former Whip, McCarthy had experience counting and rounding up votes. He's also had some successes with the conservative caucus.
"McCarthy is a contender. Being an establishment choice is a blessing and a curse," Gonzales said. "He's been working his way up the leader which puts him in position for the role but nothing is going to be handed to him on a silver platter. He's taken the traditional route but none of the traditional rules apply."
Hensarling would bring additional conservative bona fides to the position.
"He would be a credible contender," Gonzales said. "He has support within the conservative wing. But he's not being viewed as on the fringe."
Political analysts and even some conservatives question whether a tea party-endorsed leader would have the support to get elected and succeed.
"I don't think the conservative wing of the party has enough mass to get one of our own elected. We certainly have enough mass to influence the outcome," said Rep. Mick Mulvaney, R-South Carolina, a member of the conservative GOP House Freedom Caucus.
Foes within his party had been pushing to oust him if he presented any legislation that would continue to fund the government and avoid a government shutdown without stripping federal funding for Planned Parenthood.
Boehner was first elected to Congress in 1990. He became Speaker of the House in 2011.
"The right-wing of the GOP has scored a major victory, though it will probably be a hollow one," said Larry Sabato, director of the Center for Politics at the University of Virginia. "A new Speaker isn't going to be able to do much more than Boehner in countering Obama. But a right-wing driven House can be a stake in the heart of Republican presidential ambitions."
A Boehner aide told NBC News that the Speaker "believes putting members through prolonged leadership turmoil would do irreparable damage to the institution. He is proud of what this majority has accomplished, and his Speakership, but for the good of the Republican Conference and the institution, he will resign the Speakership and his seat in Congress, effective October 30."
An aide to Boehner said that the Ohio Republican had planned to serve only through the end of last year, but that the stunning primary loss of House Majority Leader Eric Cantor changed that calculation. Boehner was instrumental in and front and center during Thursday's address to Congress by Pope Francis. Boehner, who is Catholic, sat directly behind the pontiff and was visibly emotional for most of his speech.
"The only conclusion I can draw is that he's tired. He is a human being. He's been under enormous strain and pressure," said Sen. John McCain, R-Arizona, who ran for president in 2008. "I happen to have the greatest admiration and affection for him and I hope out of this that we would have a real impetus to sit down together, the different wings of the party both in House and in Senate and say 'look our goal is to elect the next president of the United States, (a) Republican candidate, now let's resolve these differences as much as possible and move forward."