“But the truth is that he hasn’t really tried,” Mr. Jesmer added. “Where is he on local talk radio? Where is the trip to Kansas to say, ‘Hey, Jerry, we’re really close on this and could use your help’? It’s what he does well, getting out there and making the case. I don’t get why he hasn’t been more engaged.”

A Republican senator, speaking on the condition of anonymity because he wanted to preserve his relationship with Mr. Trump, put it more bluntly. The president, he said, scares no one in the Senate, not even the pages.

“He has limited experience in government and politics, he lacks a deep and experienced team and his poll numbers are disastrous,” said Senator Richard J. Durbin of Illinois, the Democratic whip, as senators from both parties grappled with the sudden collapse of Republican-only health care talks.

“It’s more or less impossible to sell a program when you have those conditions,” he added.

Yet Mr. Trump still commands loyalty from about 85 percent of Republican voters, and many of them have spent seven years energetically supporting candidates who promised to demolish the health law, President Barack Obama’s central legislative accomplishment.

Mr. McConnell’s motivation for holding a vote on the deeply unpopular bill is to foster fear. Many of the nays, including Mr. Moran, want the issue to disappear; Mr. McConnell wants to put them on the record supporting the perpetuation of the Affordable Care Act.

“There are a lot of senators who have never served under a Republican president,” said Josh Holmes, a former top aide to Mr. McConnell who remains close to his team. “They are quickly learning that failing to govern when you are elected to do so has consequences.”

Mr. Trump has not displayed the same sense of urgency, Republicans say. And for all his public bluster, he despises private confrontation. He might actually be a little too nice, one top Republican Senate aide said with a laugh this week.