(CNN) -- House Speaker Nancy Pelosi said for the first time Sunday the House will move to impeach President Donald Trump if Vice President Mike Pence does not remove him.
Pelosi said the House will attempt to pass a resolution by unanimous consent Monday morning calling for Pence and Trump's Cabinet to invoke the 25th Amendment and remove Trump from office.
If the resolution doesn't pass by unanimous consent -- and it most assuredly won't given likely Republican resistance -- then the measure will be brought to the floor for a full vote on Tuesday.
The resolution will call on Pence to respond within 24 hours and, if not, the House would move to impeach the President.
"Next," Pelosi said in a letter to Democratic colleagues, "we will proceed with bringing impeachment legislation to the Floor."
"In protecting our Constitution and our Democracy, we will act with urgency, because this President represents an imminent threat to both. As the days go by, the horror of the ongoing assault on our democracy perpetrated by this President is intensified and so is the immediate need for action," Pelosi said.
House Democrats are still discussing whether a vote to impeach Trump could be Tuesday or Wednesday, per aides.
Democrats do still plan to go to the House Rules Committee first, which would adopt a rule setting the timeframe and parameters of the floor debate. It's unclear when the Rules Committee might meet. Aides expect the Rules Committee to meet Tuesday but that isn't set yet.
House Majority Whip James Clyburn said earlier Sunday House Democrats might wait until after President-elect Joe Biden's first 100 days in office to send any articles of impeachment against President Donald Trump to the Senate, a move that would give the incoming President time to tackle his agenda in Congress before the start of a time-consuming trial.
"We'll take the vote that we should take in the House, and (House Speaker Nancy Pelosi) will make the determination as to when is the best time to get that vote and get the managers appointed and move that legislation over to the Senate," Clyburn told CNN's Jake Tapper on "State of the Union."
"It just so happens that if it didn't go over there for 100 days, it could -- let's give President-elect Biden the 100 days he needs to get his agenda off and running, and maybe we'll send the articles sometime after that," the South Carolina Democrat added.
Pelosi said Friday that Democrats are prepared to move forward this week with impeaching Trump over his role in last week's deadly attack on the US Capitol if he doesn't resign. Democrats plan to introduce their impeachment resolution, which already has more than 190 co-sponsors, on Monday and sources tell CNN that the party is looking at having votes no sooner than Wednesday but they are still sorting out their plans.
The comments from Clyburn come as Democrats grapple with how impeaching Trump for a second time could impact Biden's early days in office, when he is working to get administration appointments approved in the Senate and tackling legislative priorities, like another coronavirus relief package. The incoming President's aides, meanwhile, are working behind the scenes with Pelosi and others to prevent Congress from becoming bogged down with impeachment during his early days in office.
House Democrats, on a call Pelosi held Saturday night with her leadership team, discussed the option of impeaching Trump this week and waiting until later to send the article of impeachment over to the Senate to delay the trial until after the early days Biden's presidency, according to Democrats in the party's leadership.
Pelosi said in a interview on CBS' "60 Minutes" set to air Sunday evening that she liked the idea of invoking the 25th Amendment "because it gets rid of him," but explained, "one of the motivations people have for advocating for impeachment" is to prevent Trump from holding office again.
"There's strong support in the Congress for impeaching the President a second time," she said.
Senate Majority Leader Mitch McConnell previously made clear in a memo that even if the House moved in the coming days to impeach Trump, the Senate would not return to session before January 19. That would place the start of the trial on January 20 -- the date of Biden's inauguration.
From there on out, the Senate is rendered mostly incapable of any action other than the trial until its completion, as was apparent during the first Trump impeachment trial.
By impeaching and removing Trump, even at this late stage of his term, the Senate could subsequently vote to disqualify him from ever holding federal office again, taking an extraordinary action against a former president.
Biden aides work to ensure impeachment doesn't become a distraction
While Biden has repeatedly said it's up to Congress to decide how to sanction Trump for his role in instigating the violent attack on the Capitol, CNN has learned that his advisers are working intently behind the scenes with Democratic leadership in hopes of finding a middle ground that won't hamper his new administration.
Waiting to send any articles to the Senate is one of the ideas being discussed by advisers to the President-elect, though advisers say other ideas have been under discussion this weekend, including censuring Trump in a move that may be able to draw more bipartisan support than impeachment could.
Doing nothing at all and allowing the final days of Trump's presidency to expire without punishment from Congress is not being discussed.
"The train has left the station on impeachment," an official close to Biden told CNN. "Trying to stop it would not only fail, but put Biden on the wrong foot with progressives and most Democrats across the party."
Conversations between Biden and Pelosi and many of their respective advisers have taken place throughout the weekend.
Biden is poised to roll out more specifics of his economic relief package this week in Wilmington, Delaware, where aides say he will implore Congress to act swiftly to pass the bill as one of the first acts of his presidency.
"That bill cannot and should not be delayed because of a Senate impeachment trial," an official close to Biden said.
Stream of Republicans support Trump's removal
Already, several congressional Republicans have joined Democrats in making clear they want Trump to leave office, though not all agree that impeachment is the right option.
Sen. Pat Toomey told Tapper Sunday that he thinks Trump should resign. The Pennsylvania Republican -- now the second Republican US senator to call for Trump's resignation -- had previously said he thinks Trump "committed impeachable offenses," but that he wasn't sure removing him this close to the end of his term was the right course of action.
Alaska GOP Sen. Lisa Murkowski said Friday that the President should step down from office, telling the Anchorage Daily News of Trump, "I want him out. He has caused enough damage."
Rep. Adam Kinzinger of Illinois, meanwhile, has endorsed invoking the 25th Amendment, which would force Trump's removal.
This story has been updated with additional details Sunday.