Bomb-throwers in the House Freedom Caucus derailed Kevin McCarthy’s bid for speaker in 2015.

Members of the ultraconservative, Trump-aligned group are causing major headaches for McCarthy as the California Republican makes another run for the presidency.

NBC News has not yet predicted which party will control the House, but a model of the outcome gives Republicans a slight advantage. If Republicans win, they will have a razor-thin majority.

Despite the fact that no major news organization has made the call, House Republicans have begun jockeying for leadership positions in the expectation that they will be able to seize power.

McCarthy has spent years attempting to establish himself as the next Republican House Speaker. The position carries enormous power, including the ability to control legislation on the floor and influence committee composition.

Some members of the House Freedom Caucus are outright opposed to McCarthy, while others are demanding concessions from him that would significantly limit his power as speaker.

McCarthy will need nearly every Republican’s support because the majority could be so thin. As a result, the Freedom Caucus now wields enormous power.

So far, no one has dared to challenge McCarthy. In a closed-door meeting of his members on Tuesday, he should easily win a simple majority of Republicans. Former President Donald Trump has endorsed McCarthy for speaker, as have other potential opponents and Freedom Caucus leader Rep. Jim Jordan, R-Ohio.

However, a small group of Republicans could prevent McCarthy from becoming speaker during the public vote on Jan. 3, the first day of the new Congress. McCarthy needs 218 Republican votes on the House floor — Democrats will not help — which means that fewer than a dozen conservatives could derail McCarthy’s chances and throw the process into disarray.

McCarthy attempted to project an air of inevitability on Thursday, announcing “transition teams” for the House GOP majority. Rep. Steve Scalise, R-La., who is running unopposed for majority leader, and Reps. Jordan and James Comer, R-Ky., who would chair the Judiciary and Oversight committees in a Republican majority, were among the team leaders.

However, Freedom Caucus leaders are putting the brakes on. In exchange for McCarthy’s support, they’ve presented a growing list of demands. The first could be the most damaging to McCarthy: Conservatives want him to reintroduce a rule that would make it easier to force a vote to oust a sitting speaker — a “motion to vacate.”

That’s what happened in 2015, when then-Rep. Mark Meadows, a Freedom Caucus co-founder, called for a vote to remove Republican Speaker John Boehner from power; Boehner chose to resign rather than force his members to take an unpopular vote on his speakership.

If McCarthy agrees to that demand, the threat of recall will loom over his head if he makes unpopular decisions on issues such as government spending, debt, and impeachment.

The Freedom Caucus also demands that McCarthy make legislation available for 72 hours before voting on it, and that he allow amendment votes on all bills on the floor. A delay would prevent leadership from reaching an agreement with Democrats and moving quickly to pass legislation. The demands were written down by the conservative outside group FreedomWorks, which is closely associated with the Freedom Caucus.

According to Freedom Caucus Chairman Scott Perry, R-Pa., he last spoke with McCarthy about the rule changes in September and hasn’t heard from him since. He expressed “frustration” that the GOP did not make larger gains on election night, but he was hesitant to blame a single person or McCarthy specifically.

McCarthy has been in this situation before. When he ran for speaker to succeed Boehner in 2015, members of the Freedom Caucus tried to get him to jump through similar hoops to win their votes. When he balked at their demands, Freedom Caucus members drafted GOP Rep. Dan Webster, the former speaker of the Florida House, to challenge McCarthy, giving conservatives an alternative to rally behind.