“Probably Trump wouldn’t have been the president had McConnell not decided to delay the vote on Merrick Garland,” Frank Cannon, a veteran social conservative strategist, said, referring to the majority leader’s decision to block President Barack Obama’s nominee after Justice Antonin Scalia died in 2016, saying that the vacancy should be filled by the next president.

“This is why we wanted this guy,” Mr. Cannon said, referring to Mr. Trump, who won overwhelmingly with voters who said Supreme Court appointments were the most important issue.

Mr. Cannon added that Mr. McConnell most likely views the next confirmation as equally consequential and will do whatever he can to hold a vote soon, even if the exact timing is still unclear. “This is what he sees as his legacy, and his contribution to history,” he said.