That happened when the Dems stole the two Senate Seats earlier this week.
Mitch is now literally Schumer's bitch and will do as he is told or the filibuster rule goes away.
Mitch is still in charge until 20 January, he has control over whether or there will be an impeachment. He can call for an immediate vote but make it clear to the GOP Senators that while some may defect, they are not to take Trump down or the party will suffer.