Few, if any, Republicans are expected to vote for the resolution, which was finalized in a late-night markup by the House Rules Committee at which Republicans spent nearly four hours attempting to pitch their own changes to the measure. All of the GOP amendments — which focused entirely on process — were rejected on party lines.

On substance, however, congressional Republicans have struggled to respond to the mounting pile of evidence — including damning testimony this week — showing Trump sought to persuade Ukrainian leaders to investigate his political rivals.

The kumbaya moment for Democrats follows two days of internal consternation and squabbles over both the substance of the resolution and timing of the vote.

Several moderate members were upset about the surprise rollout of the resolution Monday — some even said they found out about it from watching TV — and the disjointed messaging from leadership that followed.

Meanwhile, the multiple House committee chairmen involved in the probe were working behind the scenes to ensure they weren’t elbowed out of the process once the investigation turns public and is more firmly in the domain of the House Intelligence Committee.

The resolution, which spells out certain powers for congressional committees and the White House in future impeachment hearings, is primarily procedural. But it has taken on greater political weight with GOP campaign operatives salivating at Democrats’ first floor vote on a measure that touches on any aspect of impeachment.

In the meeting Wednesday, Speaker Nancy Pelosi reiterated to her caucus that the measure was not a vote for impeachment. Still, she acknowledged it was a solemn moment for the caucus, and asked Rep. Emanuel Cleaver (D-Mo.), a Methodist pastor, to lead the caucus in a prayer.

Rep. Jeff Van Drew has said that he is leaning against the resolution. | Alex Wong/Getty Images

“It was just ... taking a moment to say, ‘This is a big deal for our democracy in the arc of our history,’” Rep. Ann McLane Kuster of New Hampshire said as she left the meeting. “‘Gather yourself, be ready.”

“Taking this vote tomorrow is a very big deal,” Kuster added.

Only five House Democrats have not come out in support of the impeachment inquiry. So far, just one vulnerable Democrat, Rep. Jeff Van Drew of New Jersey, has said that he is leaning against the resolution on the floor. And no one expressed concerns during Wednesday’s meeting, according to multiple attendees.

“I’m sure there are some, that wasn’t expressed [today]. I think most of us recognize transparency and articulation of process is in the best interest of the country and for the institution,” said Rep. Dean Phillips (D-Minn.), who is one of several freshman who captured a previously GOP-held seat last fall.

Rep. Ben McAdams (D-Utah), one of the most endangered Democrats, said Wednesday he plans to support the measure and downplayed the significance of the vote.

“This feels like just a formalization of the process we’ve been in for some time now,” McAdams said as he left the meeting. “It’s a perfunctory vote to grant the authorization for those secure briefings to be made public to other members of Congress.”

Some vulnerable Democrats have privately worried that the Thursday floor vote could carry some risk because it marks the final vote before the House leaves for a weeklong recess during which they could face sharp questions back home about where Democrats stand on impeachment.

Pelosi and her top deputies have worked to equip Democrats with additional talking points as they depart Washington, including a fact sheet that compares the ongoing probe to past impeachments to rebut GOP criticism of an unfair process. And top Democrats have repeatedly stressed that Democrats are moving ahead only with their investigations — making no conclusion about the president’s conduct.

House investigators are continuing to question senior administration officials behind closed-doors about Trump’s effort to pressure Ukraine to open investigations into former Vice President Joe Biden, a top political rival in the 2020 election.

Two State Department officials were testifying Wednesday as part of the impeachment inquiry, revealing new details about the unusual intrusion into the U.S. foreign policy apparatus by Trump-aligned consultants.

According to copies of their opening statements obtained by POLITICO, Catherine Croft and Christopher Anderson described the unconventional efforts — which cut against the official U.S. policy toward Ukraine — in addition to Trump’s “long-held view of Ukraine as a corrupt country.”

And Lt. Col. Alexander Vindman, the first current White House official to testify, told lawmakers on Tuesday that he was so disturbed by Trump’s July 25 phone call with Ukrainian President Volodymyr Zelensky that he reported his concerns to the National Security Council’s top lawyer. It was the second time Vindman reported concerns about efforts to pressure Ukraine to investigate Biden and his family.

In addition, Vindman told lawmakers that the White House transcript of the call omitted key details and his effort to restore the missing words to the memo were ignored. The New York Times first reported the omissions.

No specific timeline for shifting to the public portion of the impeachment investigation was outlined in Democrats’ meeting, although several lawmakers have privately speculated that public hearing could start sometime before Thanksgiving, even if closed-door depositions are still ongoing.

Andrew Desiderio contributed to this report.