There may be a rule calling for a vote to call each witness, one at a time. If that is a the case, Trump might have a hard time getting witnesses. Probably won't matter in the long run; but I can see some senators, on both sides, getting tired of this crap.
“There may be a rule calling for a vote to call each witness, one at a time”
The very definition of a show trial. Selected witnesses, telling one side of the story.