Here’s the long game RE: witnesses.
If the Senate allows witness testimony regarding the HOUSE’s articles, this will set the precedent for any future impeachment. Including the one coming next year.
The House, if they disagree with (any) POTUS on any of his actions/decisions, can vote to impeach - no crime need be evident.
They won’t even need to have an inquiry. Any committee can create an article, send to the floor and the House can adopt it.
They will force the Senate to do their work for them.
I was posting some weeks ago that this precedent would set up a parliamentary system of government without a Constitutional amendment. The Senate should have dealt with this in the most severe terms.
A parliamentary system lacks our stability - look at Israel right now. However, such a change suits the Dem Party dreams for more power and control.