Speaker Kevin McCarthy didn't know whether the House could avoid a government shutdown when he met with his divided Republican conference on Saturday morning.

But behind closed doors, McCarthy's unexpected decision to take on his conservative critics quickly came together.

After GOP leaders prepared McCarthy's conference for an indefinite shutdown, his allies grew uneasy. Rep. Bryan Steil took to the mic, comparing a shutdown to a bike ride down a treacherous Bolivian mountain known as "Death Road," according to sources in the room.

If the brakes on your bike fail, Steil said, you are trained to turn into the mountain immediately, because the farther down the mountain you go, the worse the crash will be. The longer you go into a shutdown as a conservative, the Wisconsin Republican argued, the worse conservatives' options will be.

Then, one by one, vulnerable New York Republicans -- Reps. Mike Lawler, Marc Molinaro and Nick LaLota -- spoke in support of a short-term funding bill, warning of the political blowback of a shutdown and calling on their colleagues to keep the government open.

The speaker was ready to move. Turning to his conference, McCarthy asked, "Do we want to jam the Senate?" to loud cheers from his allies. McCarthy turned to an aide and asked how quickly they could go to the floor -- a "clean" stopgap bill had already been filed late Friday night.

Fifteen minutes, the aide responded.

With that, McCarthy took the only option on the table to avoid a government shutdown, relying on Democratic votes to pass a continuing resolution Saturday to keep the government funded until mid-November.

But in so doing, McCarthy opened up a fight with the right wing of his conference, which had warned him for weeks that taking this step could mean the end of his speakership.

Florida Rep. Matt Gaetz told CNN's Jake Tapper on "State of the Union" Sunday that he is planning to attempt to oust McCarthy from his role this week.

"I do intend to file a motion to vacate against Speaker McCarthy this week. I think we need to rip off the Band-Aid. I think we need to move on with new leadership that can be trustworthy," Gaetz said.

McCarthy's eleventh-hour decision to put a clean bill on the floor to fund the government -- without the border policies or deep spending cuts demanded by conservatives -- marks a new chapter in McCarthy's tenuous relationship with his right flank. It's a showdown that has been weeks, if not months, in the making, after a band of rebels denied his ascent to speakership until after 15 grueling rounds of votes in January.

McCarthy conveyed to his members that he had exhausted all other options that could pass the House -- though, in reality, it's been clear for weeks that a continuing resolution with the support of Democrats would be the only way to keep the government open. After McCarthy moved to a vote on a clean stopgap funding bill, which included additional funds for disaster relief but not for Ukraine aid, the measure quickly cleared both the House and Senate with big bipartisan majorities before the government was set to shut down at midnight.

The House's move to avoid a shutdown was a surprising change of course for McCarthy, who had been eager to avoid the showdown with his critics. But now, knowing full well he's likely to soon face a so-called motion to vacate vote, McCarthy is taking his detractors head-on -- and in increasingly combative terms.

"If somebody wants to make a motion against me, bring it," McCarthy said at a news conference after the House approved the stopgap measure. "There has to be an adult in the room. I am going to govern with what's best for this country."

McCarthy's loudest critics are determined to oust him as speaker and are strategizing over how -- and when -- to make their move. But sources close to the rebels say they want to build opposition and get the numbers on their side before they force a snap vote.

Gaetz continued to slam the speaker's leadership Saturday. "There's nothing about delaying this process that is being the adult in the room," he said. "We are at this point because Kevin McCarthy made multiple contradictory promises about the budget top line to different groups of people."

In recent days, Gaetz has been reaching out to Democrats to gauge where they stand and making his sales pitch about who he sees as a replacement for the job, floating names such as veteran GOP Rep. Tom Cole and House GOP Whip Tom Emmer. Gaetz knows he will likely need most -- if not all -- Democrats on his side to succeed.

The earliest McCarthy's critics could start the process to oust him is Monday, when the House will be back in session.

For House Democrats, it took a little bit of time Saturday -- along with the pulling of a fire alarm in a House office building -- but they ultimately chose to join Republicans to pass the stopgap funding measure.

That doesn't mean, of course, that they intend to help McCarthy keep his job as speaker. House Democratic leaders said in a statement Saturday evening they expect McCarthy to allow for a vote on a bill on supporting Ukraine.

But McCarthy's allies are confident that an overwhelming number of House Republicans support the speaker and that Democrats won't help Gaetz throw the House into chaos -- especially after McCarthy helped avert a shutdown, part of the speaker's calculation in making such a move.

GOP whiplash before clean funding bill

In the days leading up to Saturday's vote on the continuing resolution, House Republicans struggled to pass either GOP-only continuing resolutions or individual appropriations bills, measures that were loaded with conservative priorities but had zero chance of passing the Democratic-controlled Senate and wouldn't stop a government shutdown on their own.

When Republicans went into GOP conference Friday evening, leadership walked members through four options. They could try again to pass a short-term spending bill with only Republican votes, a gamble that had failed earlier in the day with more than 20 defections. They could dare Democrats to vote against a short-term spending plan. They could eat the Senate-passed bill. Or they could allow a shutdown.

By Saturday morning, it wasn't exactly clear where they'd end up, two sources said. Leadership knew what was possible, but McCarthy wanted his members to have buy-in.

One GOP lawmaker told CNN that McCarthy knew he had to demonstrate he could not pass a bill with Republican votes before reverting to a bipartisan solution. "You have to exhaust all options before doing the right thing," the lawmaker said.

That way, the speaker gave less ammunition to his critics chomping at the bit to oust him. "He hung with the exotics until they left a vast majority with no options," the lawmaker said.

The stopgap funding measure was filed at 11:52 p.m. Friday, meaning McCarthy had the bill in his back pocket, even if he didn't telegraph where he was going until the last possible second. Initially, McCarthy's team had briefed his conference on potential bills to vote on Saturday that could blunt the impact of a shutdown, such as ensuring pay for military service members or Border Patrol agents. Some lawmakers responded that other important constituents could go unpaid, which could lead to backlash.

"We walked into the conference, and I think there was a large number of us that wanted to make sure we kept the federal government open and operational," Steil said Saturday evening. "But that was not a unanimous view in the conference, and it was making sure people understood that the stopgap measure that passed today was the best option amongst a series of bad options."

Some of McCarthy's allies were surprised that the meeting didn't start by making a final pitch to vote for a short-term funding bill -- but noted the tactic helped get them there in the end.

"So either the strategy changed as a result of the comments made during open mic, or it was a strategy all along to end up there -- but don't make that your first offer and let the crowd influence that decision" Arkansas GOP Rep. Steve Womack, a senior member of the House Appropriations Committee, told CNN.

Conservative anger bubbling

The conservative hardliners in the GOP conference were dismayed at McCarthy's maneuver to keep the government open. Several blasted the speaker after Saturday's vote, though they declined to say yet whether they were ready to oust McCarthy.

GOP Rep. Ralph Norman of South Carolina would not say whether he has confidence in the speaker, though he said he was disappointed by McCarthy. "I'm disappointed. I wish we had fought. We just didn't fight," he said. "Very disappointing. Spending as usual up here. No border control."

Asked whether McCarthy should still be speaker, Norman said, "Time will tell." He also would not say whether he would vote for a motion to vacate: "We've got our hands full. We'll see what he does."

Rep. Andy Biggs, an Arizona Republican, wrote that instead of siding with his own party, McCarthy "sided with 209 Democrats" to pass the stopgap bill.

"Should he remain Speaker of the House?" Biggs posted on X, the site formerly known as Twitter.

McCarthy's allies have also been gearing up for the fight over the speakership, cognizant of the chaos that afflicted the House in the opening days of the 118th Congress when it took 15 votes for McCarthy to win the speakership.

"They can threaten and they can file. Kevin is well aware what doing the right thing for our country today meant," said one Republican allied with McCarthy. "We need to work through this. Not sure of exact play but options are available."

Some McCarthy allies have suggested they should just force the vote themselves and call Gaetz's bluff, in order to neuter the threat.

"I heard some hint at this. I don't like playing games, but we can't be held hostage by these threats," said Rep. Don Bacon, a Nebraska Republican. "If he does the motion, then we need to hit head-on and win. We need to point out that he offers no alternative, just nihilism."

Gaetz's threat of ousting McCarthy has also rankled some inside the GOP conference. One Republican lawmaker pointed to the ongoing Ethics Committee investigation into Gaetz, warning if he wasn't cleared, he could get expelled by those who want him gone.

"We want him out," the member said.

Senate Republicans step in

The delicate interplay between House and Senate Republicans became integral to McCarthy's plan, with a close friend and former House member, Sen. Markwayne Mullin of Oklahoma, playing the role of chamber-to-chamber interpreter.

Mullin attended the House conference meeting Saturday morning, answering questions about what was and was not possible -- both politically and procedurally -- in the Senate.

But the coordination didn't end there. Republican Senate Whip John Thune was also in regular communication with the speaker and in consultation with Senate Republican Leader Mitch McConnell throughout the week. On Saturday, after McCarthy announced he was moving ahead with a plan to put a continuing resolution on the floor, Thune and McCarthy chatted again with the Republican whip, providing a gut check of what could play out on the Senate floor.

The next obstacle, however, came in the form of a staring contest between the two chambers. The Senate had scheduled a procedural vote for Saturday afternoon. But McCarthy allies feared that momentum in the Senate could put the two chambers on a collision course and ultimately lead to a shutdown.

If the Senate bill advanced, McCarthy would have a harder time arguing his bill was the solution. At the very least, McCarthy allies wanted the House bill to pass first. But Democrats were deploying several dilatory tactics on the floor as they reviewed the legislation and consulted with the White House and the caucus.

The Senate's procedural vote was looming. Now it was Senate Republicans who would try to delay.

GOP senators in a closed-door lunch came to a consensus, two sources told CNN. They would need to unite and vote against advancing a bill -- which many of them planned to support -- that included $6.2 billion in aid for Ukraine. Thune and Sen. John Barrasso of Wyoming, the No. 3 Senate Republican, opposed the Senate bill, breaking with McConnell, according to a source familiar with the matter.

The senators emerged in front of the press. McConnell made the announcement. Once the Senate bill stalled, there was only one option that could pass ahead of a shutdown.

Democrats sound the (fire) alarm, but ultimately back GOP bill

Democrats had been hammering Republicans for weeks over their inability to pass government funding bills -- and McCarthy's unwillingness to consider a bipartisan solution to avoid a shutdown.

When Republicans emerged Saturday morning with the new short-term funding solution, their plan required Democratic support, under House rules requiring a two-thirds majority when bills are taken up in an expedited fashion.

House Democratic Leader Hakeem Jeffries initially demanded more time to review the House GOP's proposed measure, telling reporters that Democrats didn't trust Republicans' word on what was in the bill. House Democratic appropriators also circulated a memo raising issues with the stopgap bill.

And Rep. Jamaal Bowman pulled a fire alarm in the Cannon House Office Building shortly before the House was scheduled to vote on the government funding bill, which the New York Democrat claims was an accident.

The alarm didn't delay the bill, but it did prompt Republicans to call for his censure or even criminal charges.

Democrats had one key substantive complaint with the package McCarthy put forward: It did not include $6 billion in supplemental funding for Ukraine, unlike the Senate Democrats' stopgap funding measure.

But that wasn't enough to convince House Democrats to oppose the funding bill with a shutdown looming. A little more than three hours after McCarthy announced the House would move forward on the continuing resolution Saturday morning, it had passed the House.

Every Democrat but one -- Illinois Rep. Mike Quigley, the co-chair of the Congressional Ukraine Caucus -- voted for the measure.

"Putin is celebrating," Quigley told CNN.

The White House quickly signaled it would accept the continuing resolution, too. Top officials, including White House legislative affairs director Shuwanza Goff and senior adviser Steve Ricchetti, remained in close touch with lawmakers in both parties throughout the day amid the twists and turns.

That included direct conversations with McCarthy, officials familiar with the matter tell CNN.

In the Senate, Democrats extensively debated what to do on Ukraine aid before they took up the funding measure. Most of the Senate Democrats signed off on quickly voting on the measure. But Sen. Michael Bennet of Colorado objected over the lack of Ukraine funding, forcing Senate leaders to scramble to get the vote scheduled before the government shut down.

Bennet's objection prompted a slight delay, but the Senate gaveled back about four hours before midnight, after agreeing to a bipartisan Senate statement committing to support Ukraine. The Senate was soon voting and sent the bill to President Joe Biden's desk on an 88-9 vote.

Biden signed the measure Saturday evening with less than an hour to spare to stave off a shutdown that had seemed all but inevitable that morning.

This story has been updated with additional information.