And Kentucky's longtime senator, who has said he's in "total coordination" with the White House on the impeachment trial, reportedly isn't happy.

The New York Times reported Sunday that in his upcoming book, Bolton says Trump told him he did not want to release military aid to Ukraine until that country helped with investigations that could damage Democrats, including former Vice President Joe Biden.

Bolton's lawyer, Charles J. Cooper, told The Times he provided a copy of the book to the Trump administration on Dec. 30 to be reviewed for classified information.

A McConnell spokesman told The Courier Journal on Monday that the Senate majority leader "did not have any advance notice" that the National Security Council reportedly had a copy of Bolton's manuscript for weeks.

The GOP leader faced a handful of potential defections, but several days remained before any potential witness vote would be taken.

A decision to call more witnesses would need 51 votes to pass. With a 53-seat majority, Republicans can only afford to lose three Republicans to prevent more debate over witnesses.

McConnell has been trying to prevent a prolonged trial. Republicans were warned that subpoenaing testimony from Bolton or other witnesses could run quickly into legal challenges that could drag out for weeks.

But Sen. Mitt Romney, R-Utah, has said he wants to hear what Bolton has to say. Two other Republicans, Sen. Susan Collins of Maine and Sen. Lisa Murkowski of Alaska, also want to hear from more witness.

The White House has blocked its aides from appearing in the impeachment proceedings and would almost certainly claim some sort of executive privilege or national security objections over Bolton testifying.