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.

From the moment McCarthy was elected speaker, it was clear that his ability to keep that job could depend on Democrats.

To get elected on that 15th ballot in January, McCarthy had to agree to a series of rules that made him a profoundly weak speaker -- including the provision allowing a single member of the House to call for a vote to oust him (the now-famous "motion to vacate"). But while it takes just one member to call for such a vote, it requires a majority to actually remove the speaker.

McCarthy could survive a rebellion from a handful of renegade Republicans -- but he could not survive such a rebellion if Democrats go along with it.

Gaetz has said he expected Democrats to save McCarthy. Many others did too.

As recently as Tuesday morning, House Minority Leader Hakeem Jeffries suggested a way out of this for McCarthy. In an interview on MSNBC, he said House rules should be changed so that a single member could not force a vote on removing the speaker. Jeffries could deliver the votes to save McCarthy's job and the votes to change the rules to make it impossible for Gaetz to pull off a stunt like this again.

But Democrats would have a price for doing that. What would McCarthy offer in return? An end to the impeachment inquiry in President Joe Biden and his family? A guarantee that McCarthy honors the deal he struck on spending with the White House? Power sharing?

McCarthy has developed a cordial relationship with Jeffries, but he signaled no willingness to give Democrats anything in exchange for keeping the job.

In fact, McCarthy's actions have made it virtually impossible for Jeffries to throw him a lifeline. The speaker unilaterally launched the impeachment inquiry and just Saturday infuriated Jeffries by attempting to jam Democrats on a bill to keep the government funded for 45 days.

Back in January -- and again last month on impeachment -- McCarthy showed he was willing to do almost anything to appease his right-wing critics to get and keep his job. That worked for a while -- but it has made it virtually impossible to get Democrats to save him now.

-ABC News Chief Washington Correspondent Jonathan Karl