Just in: Nancy Pelosi is expected to announce launch of formal impeachment inquiry Tuesday afternoon

House Speaker Nancy Pelosi is expected to announce a formal impeachment inquiry later Tuesday, multiple sources on Capitol Hill tell CNN.

Pelosi had earlier said she would make an announcement at 5 p.m. ET.

Amid dozens of Democratic lawmakers opening the door to impeachment proceedings, Pelosi is consulting Tuesday afternoon with the six House Democratic leaders to discuss their presentation to the caucus later in the day, Democratic sources familiar with the issue say. The speaker has been on the phone with her colleagues over the last several days to take the temperature of the whistleblower complaint as she decides whether to embrace impeachment, Democrats say.

At an Atlantic Ideas Festival event in Washington, Pelosi declined to weigh in on specifics when asked about impeachment.

"It's really sad to think that our President would perform an impeachable offense," Pelosi said at the event. "It's hard to say you've gotten to that place. But what would be an impeachable offense would be that which is proven in an investigation."

CNN reported earlier Tuesday that Pelosi is also expected to put a resolution on the House floor Wednesday to address reports that Trump pushed Ukraine's President to investigate former Vice President Joe Biden and his son, amid growing calls to start the impeachment process, according to sources.

What that resolution will specifically say is still being worked out. A Democratic leadership aide told CNN that key committees are currently working on the language.

A source added that Pelosi wants to do this before Thursday, when acting Director of National Intelligence Joseph Maguire is scheduled to appear before House Intelligence Committee, in hopes of pressuring him to reveal the details of the whistleblower complaint against Trump.

Pelosi is encouraging members of her caucus to state their impeachment position now in order to show there is a groundswell in the caucus. She is also conveying that message to freshmen.

This comes as Pelosi will meet with key committee chairmen who are leading investigations into Trump ahead of a full caucus meeting Tuesday afternoon, according to Democratic sources, in what appears to be a crucial day for the party and their strategy on whether to impeach the President.

A senior House Democratic aide said some Democrats have raised the idea of setting up a select committee to investigate all the allegations of wrongdoing against Trump since now it appears that the issues — like the Ukraine scandal — cross the jurisdiction of several committees.

Some Democrats are likely to endorse this move publicly, but Pelosi has not decided on this yet, Democratic sources said.

Setting up a panel would be complicated and time-consuming, so many Democrats are skeptical they would go this route. But it's another sign of the growing focus on impeachment in the House Democratic Caucus.

In an interview with CNN Monday night, Pelosi declined to say whether she would fully endorse initiating an impeachment inquiry when she meets with the caucus Tuesday.

But she left little doubt the developments around the whistleblower's complaint had dramatically escalated the standoff with Trump and a move toward impeachment proceedings was all but certain.

"We will have no choice," Pelosi said of ultimately getting behind an impeachment inquiry.

Tide changing for Pelosi allies and vulnerable House freshmen

Civil rights icon Rep. John Lewis on Tuesday announced his support for impeachment proceedings, arguing that "now is the time to act" and any delay "would betray the foundation of our democracy."

"We will never find the truth unless we use the power given to the House of Representatives and the House alone to begin an official investigation as dictated by the Constitution," the Georgia Democrat said in a speech on the House floor. "The future of our democracy is at stake."

Rep. Lewis joins Dems calling for impeachment inquiry 01:04

Some of Pelosi's closest allies, including House Reps. Rosa DeLauro of Connecticut and Debbie Dingell of Michigan, have signaled their support for impeachment proceedings — a significant indicator that the speaker could be moving closer to backing the divisive political procedure.

Another crucial development has been multiple high profile freshmen Democrats in districts Trump won in 2016 either coming out publicly to fully endorse the House Judiciary Committee's impeachment inquiry or at least opening the door to proceedings, citing Trump's actions as forcing them to act.

One of those freshman Democrats, Rep. Mikie Sherrill of New Jersey, stressed on CNN "New Day" Tuesday that "none of us ran on impeaching the President." But she argued that the allegation that Trump might have tried leveraging foreign military aid to advance his reelection efforts was "just a line that I think was too much for all of us."

Pelosi has cited the House members in GOP-leaning districts as part of her hesitance to embrace impeachment, and the groundswell of statements over the past 48 hours could signal a tipping point in the political calculus.

Everything we know right now about Trump's call to Ukraine

"If investigations confirm recent reports, these actions represent impeachable offences that threaten to undermine the integrity of our elections and jeopardize the balance of power within the federal government," Rep. Haley Stevens of Michigan said in a statement Tuesday. Stevens had told CNN last month that she had "mixed reviews from the people of my district" on the issue of whether to move forward with impeachment proceedings.

So far, as many as 158 House Democrats have publicly stated their support for an impeachment inquiry into Trump, according to a CNN count, and that doesn't include the House Democrats who've said in recent days that the President's behavior is a turning point in Democrats' oversight into the administration.

Pelosi has, for months, resisted pursuing impeachment because she has sought to protect vulnerable Democrats in GOP-leaning districts who could face voter backlash.

Rep. Jamie Raskin of Maryland, a member of House Judiciary, told CNN on Tuesday morning that he believes articles of impeachment are "inevitable" and said there's a "growing clamor throughout the Democratic caucus" to deal with Trump's "reckless and lawless" behavior.

Some holdouts remain

But some vulnerable Democrats in 2020 are still treading cautiously on the issue.

Rep. Ben McAdams of Utah told CNN on Tuesday that he's "considering" impeachment, but didn't want to discuss the issue further.

"Before making any judgments, I want to know the facts of what occurred between the President and Ukraine," McAdams said. "I share Sen. (Mitt) Romney's view that If the President used his position to pressure a foreign power to dig up dirt on a rival for his own personal gain, it would be deeply troubling. I believe it would be a betrayal of the loyalty owed to our country and the Constitution."

Rep. Max Rose, another endangered House Democrat, told CNN that he has not moved off his opposition to impeachment, but argued that "we have to get to the facts" of the allegations.

"It is impossible to not take these allegations seriously. It is a national security matter," the New York Democrat said Tuesday on Capitol Hill, adding, "It's incredibly serious ... what I'm not going to do is jump to make another declaration."

Asked if that meant he is opposed to moving ahead on impeachment, Rose said, "My current position right now is clear, but that is not a justification to not take these points as seriously as possible."

CNN previously reported that Trump pressed Ukrainian President Volodymyr Zelensky in a July 25 call to investigate former Vice President Joe Biden's son, Hunter, according to a person familiar with the situation.

There has been no evidence of wrongdoing by either Joe or Hunter Biden.

That call was also part of a whistleblower complaint submitted to the Intelligence Community Inspector General, which hasn't been shared with lawmakers despite calls from Democrats.

Trump acknowledged on Sunday that he discussed the former Vice President Joe Biden in a phone call over the summer with Ukraine's president, but denied doing anything improper.

CNN confirmed that Trump asked his acting chief of staff Mick Mulvaney to put a hold on millions in military aid to Ukraine roughly one week before a call with Zelensky, two senior administration officials said on Monday. The Washington Post first reported this.