Donald Trump was in a state of shock: He had just fired his campaign manager and was watching the man discuss his dismissal at length on CNN. The rattled candidate’s advisers and family seized the moment for an intervention.

Joined by his daughter Ivanka and her husband, Jared Kushner, a cluster of Trump’s confidants pleaded with him to make that day — June 20 — a turning point.

He would have to stick to a teleprompter and end his freestyle digressions and insults, like his repeated attacks on a Hispanic federal judge. Paul Manafort, Trump’s campaign chairman, and Gov. Chris Christie of New Jersey argued that Trump had an effective message, if only he would deliver it. For now, the campaign’s polling showed, too many voters described him in two words: “unqualified” and “racist.”

Trump bowed to his team’s entreaties, according to four people with detailed knowledge of the meeting, who described it on the condition of anonymity. It was time, he agreed, to get on track.

Nearly two months later, the effort to save Trump from himself has plainly failed. He has repeatedly signaled to his advisers and allies his willingness to change and adapt, but has grown only more volatile and prone to provocation since then, clashing with a Gold Star family, making comments that have been seen as inciting violence and linking his political opponents to terrorism.

Advisers who once hoped a Pygmalion-like transformation would refashion a crudely effective political showman into a plausible American president now increasingly concede that Trump may be beyond coaching. He has ignored their pleas and counsel as his poll numbers have dropped, boasting to friends about the size of his crowds and maintaining that he can read surveys better than the professionals.

In private, Trump’s mood is often sullen and erratic, his associates say. He veers from barking at members of his staff to grumbling about how he was better off following his own instincts during the primaries and suggesting he should not have heeded their calls for change.

He broods about his souring relationship with the media, calling Manafort several times a day to talk about specific stories. Occasionally, Trump blows off steam in bursts of boyish exuberance: At the end of a fundraiser on Long Island, New York, last week, he playfully buzzed the crowd twice with his helicopter.

But in interviews with more than 20 Republicans who are close to Trump or in communication with his campaign, many of whom insisted on anonymity to avoid clashing with him, they described their nominee as exhausted, frustrated and still bewildered by fine points of the political process and why his incendiary approach seems to be sputtering.

He is routinely preoccupied with perceived slights, for example raging to aides after Sen. Marco Rubio of Florida, in his re-election announcement, said he would stand up to the next president regardless of party. In a visit to Capitol Hill in early July, Trump bickered with two Republican senators who had not endorsed him; he needled Rep. Peter T. King of New York for having taken donations from him over the years only to criticize him on television now.

And Trump has begun to acknowledge to associates and even in public that he might lose. In an interview on CNBC Thursday, he said he was prepared to face defeat.

“I’ll just keep doing the same thing I’m doing right now,” he said. “And at the end, it’s either going to work, or I’m going to, you know, I’m going to have a very, very nice, long vacation.”

Jason Miller, a spokesman for Trump, said the Republican nominee was still determined to win, and dismissed accounts that he was downcast. Miller pointed to the crowds Trump attracts as a sign of strength.

“Behind the scenes we have a very motivated and very focused candidate in Donald Trump, who knows what he needs to do to win this race,” Miller said.

People around Trump and his operation say they are not ready to abandon hope of a turnaround. But he is in a dire predicament, Republicans say, because he is profoundly uncomfortable in the role of a typical general election candidate, disoriented by the crosscurrents he must now navigate and still relying impulsively on a pugilistic formula that guided him to the nomination.

His advisers are still convinced of the basic potency of a sales pitch about economic growth and a shake-up in Washington, and they aspire to compete in as many as 21 states, despite Trump’s perilous standing in the four states — Florida, Ohio, Pennsylvania and North Carolina — likely to decide the election.

Charles R. Black Jr., an influential Republican lobbyist supporting Trump, said the campaign was in a continuing struggle to tame him.

“He has three or four good days and then makes another gaffe,” Black said. “Hopefully, he can have some more good days.” Of Trump’s advisers, Black said, “They think he is making progress in terms of being able to make set speeches and not take the bait on every attack somebody makes on him.”

Trump’s advisers now hope to steady him by pairing him on the trail with familiar, more seasoned figures — people he views as peers and enjoys spending time with, like former Mayor Rudolph W. Giuliani of New York and former Gov. Mike Huckabee of Arkansas.

Giuliani, who campaigned with Trump early last week, said he did not see the candidate as unmoored or unhappy. If anyone was disconcerted, Giuliani suggested, it was the people steering his campaign.

“He doesn’t seem to be as unnerved by these things that go wrong as the people around him,” Giuliani said. Still, he allowed, “I think it is true that maybe it took him a little while to realize that we’re moving from a primary campaign to a presidential campaign.”

Trump’s advisers believe he is nearly out of time to right his campaign. On Tuesday, hours before his explosive comment about “Second Amendment people” taking action if Hillary Clinton is elected, his brain trust reassembled again at Trump Tower in a reprise of their stern meeting in June.

They again urged Trump to adjust his tone and comportment. The top pollster, Tony Fabrizio, gave an unvarnished assessment, warning that Trump’s numbers would only move in one direction, absent a major change.

Trump, people briefed on the meeting said, digested the advice and responded receptively.

It was time, he agreed, to get on track.