They seem to think he encouraged an invasion of the Capitol. Not that they need a reason. Democrats in Congress, and anti-Trump Republicans, don't need a reason now, any more than they did when they impeached him for a phone call.
Lots of freepers seem to think the Senate won't convict because of timing rules, as if they care about rules, or because there aren't sufficient votes. Toomey (R-PA) just went on record saying impeachable offense was committed. Two-thirds of the Senate will be found to convict and no pesky timetable is going to stop them.
The House could vote to impeach him (again) on Monday, slam bam, but the Senate must afford the President a trial and that would certainly take more than a week to get set up, hold it, etc.
Besides Turtle said we’re adjourned until Jan 20. Can’t impeach and remove from office after his term is up.