If there are no witnesses to provide then you'll have to explain why Trump is explicitly refusing to provide them. The answer is simple; cowardice and guilt. An innocent man doesn't hide behind 'executive privilege', or command his minions to disobey Congress.
Your side could have filed suit and decided you didn't want to and took your chances and lost.
Look, sometimes you win and sometimes you lose and with Trump at the helm, Lucy once again pulled that football away at the very last second and peanuts fell flat on his back. You wasted 3 months not going to court because, quite frankly, your side knew you would get hammered. Now, Ma and Pa Kettle are feigning upset that even though Trump has asserted executive privilege, he should forget all about that and let Ma and Pa get their way.
Speaking of which,these old fossils have always gotten their way and have't experienced shame, humiliation and defeat on this scale EVERRR!
Our side knows what is really happening. Ma Kettle knows her goose is OVER cooked and she has nothing at all to show the Senate, She is trying to buy some time for maybe a Christmas Miracle and for Santa Claus to drop some "evidence" in that empty bag. McConnell has given their collective of arrogant assassins the finger and told them that their kangaroo court is done, over, finiti. The Senate will take over if and when she delivers the bag of air. The trial will be smooth and efficient and take maybe a half hour or so. Here is how it will go after pleasantries are exchanged, There will be no speeches from constitutional scholars or arrogant Vidman types:
Q, to Trump haters: I see you are holding a bag. Is that for the court to see?
A FROM Trump haters: Yes your honor
Q. to Trump haters: Please hand that to the clerk, Clerk. Please take the contents out so that I can review them
(Clerk looks through bag, shakes it, turns it upside down and inside out and finds it empty)
Q, to Trump haters: I expected to see evidence. You brought an empty bag
A. From Trump haters: Yes, your honor but we did get testimony from others that they didn't much like Orange Man
Q, to Trump haters: The court asked for fact witnesses also. Please present them.
A. FROM Trump haters: Um,your honor, we have someone who said he presumed, assumed, speculated and did the jig.
Q. to Trump haters: Do you have anything else to present to the court in the way of FACTS or first hand knowledge>
A. From Trump haters: You want like REAL facts and stuff? We thought he could be impeached because
Q. to Clerk; Please take Ma and Pa Kettle and evil eyes Schiff directly to jail for impersonating someone with half a brain because you couldn't make one brain out of all three of them. Case DISMISSED!