All that shouting they did about how unfair the process was because they couldn't call witnesses means a majority of the public wants witnesses at the Senate trial.
They're sunk either way.
If they vote to call witnesses, the truth will come to light.
If they vote against witnesses, a majority of Americans will view an acquittal as meaningless.
*A phrase I learned from Ambassador Sondland, who testified that Trump wanted Zelensky in a “public box" (and that everything depended on Zelensky making an announcement.)