When this reaches the senate, the GOP senators can go on record as to whether they will demand the truth from those who can exonerate him or support continuing to let them hide.
Sadly, there is no way the GOP Senate will allow any White House cabinet member or Giuliani to testify. They know that either they will tell the truth which would be devastating to Trump, or they would lie under oath- a criminal act. And as Nebraska said, its pretty odd because these witnesses could supposedly exonerate Trump.
One other option, which is the most likely in my opinion if they were to testify, they would claim the 5th or they would claim Executive Privilege, which to average Americans would look suspicious, especially given that Trump has commented he did nothing wrong and these folks would presumably exonerate him. It is because of the possibility they would not answer questions, that they will not be called, in my opinion.
Yes that is a possibility but I don’t think McConnell would call them up just to take the 5th and make the Trump enterprise look even more guilty.
Unless, Collins, Romney and Murkowski stand united to demand White House cabinet members as witnesses, I really doubt it will happen. And I’m pretty certain those three will not push that hard.