Watching Rudy will be interesting here. He has no immunity and no deference as he is not a public official. So what role he played might be critical in the quid pro quo aspect of this. If there is evidence he did so....
Does he turn and run to save his own hide?
Does he blather incoherently ? (Ok, that's a given)
Does he refuse to answer any questions to try to protect Trump?
See, the thing is, Trump shows loyalty only to the point where he gets a whiff you might turn on him. Just an inkling and he pulls the rip chord. The weakness here is Rudy. The Dems should insist he testify and disclose what Trump told him to do about Ukraine and Biden, what he was tasked with attempting to get done. Trump will then distance himself "I don't control Rudy, he did his own thing..." and then Rudy will know he is next in line to have his legs chopped of by Trump.