Rep. Matt Rosendale, R-Mont., just announced his support for the motion to oust McCarthy.

"I have kept my promise to the people of Montana by voting to make us energy-dominant again, secure our border, cut spending, and to put an end to the social experiment being inflicted on our military," Rosendale wrote in a post to X, formerly known as Twitter.

"Unfortunately, Kevin McCarthy violated his promise to the American people and the Republican Conference by working against them repeatedly and supporting ploys to aid the Left. This demonstration of failed leadership is exactly why I plan on supporting the motion to vacate this afternoon," Rosendale added.

The five other Republicans who've said they want McCarthy removed are Rep. Matt Gaetz, Rep. Bob Good of Virginia, Rep. Andy Biggs of Arizona, Rep. Eli Crane of Arizona and Rep. Tim Burchett of Tennessee.

-ABC News' Katherine Faulders

McCarthy presided over the House opening prayer -- with his head bowed, eyes closed and hands clasped -- possibly for the final time as his speakership hangs in the balance.

"On this day, may we sacrifice our inclination for contempt and instead initiate kindness," Chaplain Margaret Kibben said as she offered the prayer.

"Loosen our grip on judgment and instead may we grab hold of a generosity of spirit. May we foreswear our grudges and commit instead to exercise forbearance. Hold us accountable that our arguments will hold forth your righteousness and not ring hallow in our rightness."

During a more than two-hour caucus meeting, Democrats were strongly encouraged to vote to not support Speaker McCarthy as he fights for his job, sources tell ABC News.

"It is now the responsibility of the GOP members to end the House Republican Civil War," House Minority Leader Hakeem Jeffries said in a statement. "Given their unwillingness to break from MAGA extremism in an authentic and comprehensive manner, House Democratic leadership will vote yes on the pending Republican Motion to Vacate the Chair."

Several Democrats said they don't plan to bail McCarthy out.

"We're not voting in any way that would help save speaker McCarthy," Rep. Pramila Jayapal, D-Wash., said.

Vice Chair of House Democratic caucus Rep. Ted Lieu, D-Calif., said, "the leadership put out the facts and the caucus heard from a lot of members… we need a functioning government and speaker McCarthy has shown he cannot govern."

A motion to vacate has only ever been voted on once, in 1910, in an effort to boot then-Speaker Joseph Cannon. The effort failed.

In 2015, then-Rep. Mark Meadows filed a resolution to force a vote on then-Speaker John Boehner’s leadership. But because Meadows didn’t introduce it on the House floor, it wasn’t taken up for consideration.

While history shows previous such efforts over the years have always failed -- it's possible this one could succeed.

Read more from ABC News' Tal Axelrod here.

Gaetz spoke to reporters outside the Capitol just moments after his motion to vacate succeeded.

"The stages of grief are in progress," he said.

The Florida Republican floated names for who could become the next speaker. On his list were House Majority Leader Steve Scalise, House Majority Whip Tom Emmer and Oklahoma Rep. Kevin Hern.

Gaetz said he will "absolutely not" put himself forward for speakership.