Majorities of Americans believe the Senate trial must include witnesses and documents; 66% want to hear from Bolton (39% of Republicans, 71% of independents, 91% of Democrats).
His willingness to testify is among the Pelosi's prizes by delaying transmission of impeachment articles. He called Giuliani a 'hand grenade' and had proximity to Trump during the Ukraine scandal; his testimony will send shock waves through the GOP.
Republican senators want witnesses in the Senate trial; Mitch tries to quash it. Trump fears that as many as four GOP senators vote in favor of hearing from witnesses. So as 2/3rds of the public shows interest in hearing from Bolton and several Republican senators mull voting in favor of witness testimony, McConnell is stuck trying to figure out how to appease members mired in vulnerable reelection bids while ensuring that no witnesses are heard from.