WASHINGTON — President Trump thought he could sell balky Republican senators like Ron Johnson of Wisconsin on the Senate health care bill through pleasantries, cajoling and, ultimately, some Oval Office muscle.
But Mr. Johnson could not be charmed. He could not be outbargained. And he could not be scared into supporting the measure for the sake of a president whose inability to bend fellow Republicans toward his political will has become a liability for his young presidency.
As the brash Mr. Johnson reminded one associate recently, while Mr. Trump may have stunned the political world in 2016 by winning Wisconsin in the election, Mr. Johnson got 76,000 more votes in the state.
Fear is perhaps the most powerful motivating force in politics, and fear of a powerful president is the surest lever to move a lawmaker from a “no” to a “yes” on a presidential priority. But over the past month, Mr. Trump scared no one into supporting the bill to repeal and replace the Affordable Care Act. He has proved simply too unpopular nationally — polling at 36 to 40 percent approval this week — too weak in many senators’ home states, too erratic and too disengaged from the details of governing to harness his party, as other new presidents have.
Mr. Johnson, still angry at the Republican establishment for abandoning his long-shot re-election bid, may come around when Senator Mitch McConnell, the majority leader, holds a make-or-break procedural vote next week in a bid to revive the health care effort.
But the votes of other senators have become more elusive. They have come to believe that their constituents, even the most conservative ones, are more loyal to them than to Mr. Trump.
The starkest demonstration of Mr. Trump’s weakness came on Monday when Mr. McConnell and his stunned team learned that Jerry Moran, a typically reliable and evenhanded conservative from Kansas, felt safe stiff-arming Mr. Trump on his top legislative priority, announcing that he opposed the bill.
“Right now, nobody’s afraid of Trump, and that’s a real problem,” said Rob Jesmer, the former executive director of the National Republican Senatorial Committee and once a top aide to Senator John Cornyn of Texas.
“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.
After Speaker Paul D. Ryan canceled the first scheduled vote for a repeal-and-replace bill, two top advisers urged Mr. Trump to show wayward House members that they would pay a price for challenging the president. But Mr. Trump ultimately stood by the leadership and declined to target anyone.
Mr. Trump expressed his pique to aides when Senator Rand Paul, a Kentucky Republican, announced his opposition to the bill on the grounds that it preserved too many elements of the existing law. But when it came time to make the case personally, Mr. Trump opted for a putter over a cudgel.
Mr. Trump asked Mr. Paul to play golf — to clear his head — offering to play with him personally, if it meant getting him off TV bashing the Senate bill, according to three Republicans with knowledge of the exchange.
The president’s attempts to use force have backfired.
His team has talked with a possible Republican challenger to Senator Jeff Flake, Republican of Arizona, who has raised questions about the bill. So far, Mr. Flake has not changed his behavior.
When Dean Heller, a Nevada Republican who opposed the Senate’s first repeal-and-replace effort and who faces a tough re-election battle next year, a Trump-allied political action committee ran ads against him. But under pressure from Senate leadership, Mr. Trump himself expressed his desire to have the ads pulled from the airwaves, and they came down soon after.
And Nevada’s Republican governor, Brian Sandoval, who is far more popular in his state than Mr. Trump, never backed off his opposition to the health measure, even after a phone call from the president and a series of one-on-one meetings with senior administration officials at the National Governors Association meeting last weekend in Rhode Island.
Mr. Trump, to exert pressure, sat Mr. Heller next to him during an awkward opening at a White House meeting on Wednesday with Republican senators convened to rekindle interest in voting on a clean repeal of the health care law before the August recess.
The president began with a barbed joke, urging the senator to back his third push for a Senate repeal.
“You weren’t there. But you’re gonna be,” the president said. “You’re gonna be. Look, he wants to remain a senator, doesn’t he? And I think the people of your state, which I know very well, I think they’re gonna appreciate what you hopefully will do. Any senator who votes against starting debate is really telling America that you’re fine with Obamacare.”
Other senators were visibly stunned by the lightly veiled threat.
Mr. Heller blushed, laughed and remained politely noncommital.