Mr. McConnell has told colleagues and the White House that he does not want witnesses called, seeing it as an opening for uncertainty during the trial. Mr. Trump, in private discussions, has told advisers that he understands Mr. McConnell’s argument, but at times he has said that he wants witnesses. Source

House and Senate Dems need to keep up the pressure until Trump is demanding that witnesses testify. There needs to be a scorched earth campaign that ends in Trump on his knees begging to testify about his perfect call (although history suggests that Trump will cut and run before that happens).