At a Senate GOP luncheon this week, McConnell warned his colleagues against calling witnesses. “Mutually assured destruction,” he said, according to a Republican in the room.

McConnell is not sure Republicans have enough votes to only call Trump’s preferred list, the person said. Any agreement to call a witness would require 51 votes, and if Democratic votes were needed to end an impasse among Republicans, Senate Minority Leader Charles E. Schumer (D-N.Y.) would demand his own list of witnesses as part of any compromise.

Under McConnell’s thinking, this could possibly mean calling Vice President Pence and top White House aides, such as acting chief of staff Mick Mulvaney, to testify.

“Witnesses would be a double-edged sword,” Sen. Mike Braun (R-Ind.) said.