Pelosi sent a letter Sunday to her fellow Dems, and she says that on Monday ... the Majority Leader in the House, Rep. Steny Hoyer, will ask for unanimous consent on a resolution demanding Pence assemble the other cabinet members, and invoke the 25th Amendment on Trump ... which would remove him from his post, and have Pence in as acting Prez.
If they meet any roadblocks in getting that unanimous consent, Speaker Pelosi says they'll bring it to a floor vote on Tuesday. She also says this, "We are calling on the Vice President to respond within 24 hours".
If Pence stonewalls on invoking the 25th Amendment, the House will begin impeachment proceedings later this week. She says, "In protecting our Constitution and our Democracy, we will act with urgency, because this President represents an imminent threat to both".