WASHINGTON — Key Republican senators who could tip President Donald Trump’s impeachment trial toward summoning more witnesses played an over-sized role in the final hours of debate Thursday night with pointed questions ahead of crucial votes.

A vote on witnesses, expected Friday, could lead to an abrupt end of the trial. Or it could bring days, if not weeks more argument as Democrats press to hear testimony from former national security adviser John Bolton and others.

Any four Republicans could join with Democrats to demand taking more time for testimony.

Sen. Lisa Murkowski of Alaska drew a reaction when she asked simply: “Why should this body not call Ambassador Bolton?”

GOP Sen. Lamar Alexander of Tennessee captured attention just before the dinner break when he questioned partisanship in the proceedings thus far.

Sen. Susan Collins, the Maine Republican whose vote on witnesses was considered in the balance, wanted to know why House Democrats withdrew a subpoena for a deputy national security adviser they wanted to hear from in the impeachment inquiry.

Alexander consulted with a key staff aide to Majority Leader Mitch McConnell, and met with Murkowski privately. Republican Sen. Mitt Romney of Utah is among those being watched.