“But Mulvaney’s going to claim executive privilege and it will be tied up in courts,” Murphy said.

Mulvaney was front and center during the first full day of the House manager's arguments, particularly the television clip of him confirming a quid pro quo that Ukraine aid wouldn’t be delivered without an investigation announced into Democrats — a claim which he later walked back.

Whether the Senate will call any witnesses at all is still in doubt, with a key procedural vote scheduled for next week on whether to subpoena new witnesses and documents. Votes to secure documents and testimony from Mulvaney, Bolton and others failed on Tuesday and Wednesday on party lines.

Unlike most potential witnesses in the Ukraine saga Democrats, Bolton has publicly confirmed he would be willing to testify in the Senate trial if subpoenaed. But he is viewed with some suspicion by the opposition party.

“I have low expectations for Bolton. I think we have to hear from him, but I think his next 20 years are tied up in making money and donations in book sales for Trump supporters,” Murphy said. “But if there’s a chance for him to be very clear about what the president said to him? Maybe. There is this one meeting between he and Trump in which, if he doesn’t claim executive privilege or ignores protections from the president, you could have some explosive testimony.”