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.

Now-former Speaker McCarthy addressed reporters from Capitol Hill on Tuesday night where he looked back at his years in Republican leadership, touted his record -- and struck an optimistic if ambiguous note about his future.

"I believe I can continue to fight," McCarthy said, while noting that he will not run again for speaker after he lost a historic vote on the motion to vacate earlier in the day.

"My goals have not changed. My ability to fight is just in a different form," he said, later adding, "I'll never give up on the American people. That doesn't mean I have to be speaker."

McCarthy also swiped at the conservative rebels who ousted him from his role -- stressing that they were just 4% of the GOP conference -- and claimed that Gaetz was acting out of a personal sense of grievance in pushing him out, which Gaetz denies.

Despite the defeat he suffered from within his own party, McCarthy sounded largely sanguine about his political career.

He contended that the Democratic minority deciding to vote against him had made a "political decision" that undercut the ability of the House to govern.

"My fear is the institution fell today," he said.

Still, in largely valedictory remarks, he pointed back to work to cut government spending, expand his party's base and increase their majority in Congress, including by electing more women and minorities.

"I feel fortunate to have served the American people," he insisted. "I leave the speakership with a sense of pride, accomplishment and, yes, optimism."

-ABC News' Adam Carlson