My theory has the House deferring the impeachment vote to October 2020, when they still control the House.
That would get them the impeachment they want while likely preventing the Senate from holding a trial after the election. Also, the Senators don't have to worry about a Senate trial affecting their campaign schedules.
Yes, the Democrats would have to keep the House in 2021 to try again, but they would have to start over in the new House.
-PJ
BS