Campaign advisers to Donald Trump, concerned that his focus and objectives had dissolved during the first presidential debate Monday, plan to more rigorously prepare him for his next face-off with Hillary Clinton by drilling the Republican nominee on crucial answers, facts and counterattacks, and by coaching him on ways to whack Clinton on issues even if he is not asked about them.

Whether he is open to practicing meticulously is a major concern, however, according to some of these advisers and others close to Trump.

While analysts from both parties and several focus groups declared Clinton the winner of the debate, Trump tried to claim that title for himself on Tuesday, citing unscientific online surveys, and told his advisers that he believed he had done well in the first half-hour of the 90-minute event.

A delicate approach to the candidate is now in the works. Before his advisers can shape Trump’s performance for the next debate, on Oct. 9 in St. Louis — which, contrary to speculation, he does plan to attend, a top aide said — they need to convince him that he can do better than he did in the first one and that only a disciplined, strategic attack can damage Clinton with voters. Advisers said that Trump had been prepped to handle Clinton’s attacks on Monday but did not effectively execute responses to them.

Republican allies of Trump said he needed to exploit what they see as her vulnerabilities.

“People know who Hillary is — they’ve seen her and heard about her for 30 years,” said Sean Spicer, chief strategist for the Republican National Committee, who works for the Trump campaign part time. “And what needs to be done next is that he is seen as the element of change.”

At a rally on Wednesday in Council Bluffs, Iowa, Trump bragged that he had won the debate by “a landslide.” He said he did not think Clinton “did well in the debate at all,” and noted the feedback that he received from people as he took the stage for the rally.

“I just walked in, and I saw so many great people, and they said, ‘Wow, you did so great in the debate,’” he said. “And we understand that. We understand that.”

Even as Trump’s advisers publicly backed him and praised his debate performance, they were privately awash in second-guessing about why he stopped attacking Clinton on trade and character issues and instead grew erratic, impatient and subdued as the night went on. In interviews, seven campaign aides and advisers, most of whom sought anonymity to speak candidly, expressed frustration and discouragement over their candidate’s performance Monday night.

They blamed his overstuffed schedule, including a last-minute rally in Virginia that was added days before the debate. They blamed the large number of voluble people on his prep team, including two retired military figures with no political background. And they blamed the lack of time spent on preparing a game plan in the first place.

Trump, for his part, sought to blame everything but himself. During an appearance on Fox News on Tuesday, he charged that the moderator, Lester Holt of NBC News, had become overly aggressive with him — although he inaccurately said that Holt had questioned him over a 1973 federal discrimination lawsuit against Trump’s company. (Clinton had raised the lawsuit question.) He also suggested that his performance was related to a faulty mike — even though he was perfectly audible during the telecast — and that he may have been the victim of sabotage.

And at a rally in Florida later that evening, he ripped Clinton in scathing terms that he declined to use when they were face to face.

But Trump’s lack of facility as a one-on-one debater was glaring at times, such as his inability to challenge Clinton’s judgment over the attacks on the American diplomatic mission in Benghazi, Libya. He protested on Fox News that he could not find a way to bring up Benghazi, saying, “Don’t forget, you are asked a question as to progress or as to something, and it’s hard to get off to Benghazi sometimes the way the questions were framed.”

Clinton, who prepared at length for the debate, was far more deft at unnerving her opponent, finding a way during an exchange about trade to bring up a loan that Trump had received from his father. Topics during general election debates are often inserted at prime openings by the candidates themselves, rather than by the moderators, whom Trump relied on during the primary debates to set the tone.

The shape and schedule for Trump’s next round of debate preparations are still under discussion, his advisers said.

Some of the advisers want to practice getting under his skin, as Clinton did, to gauge his response, but they offered no details about doing so. Others wanted practice sessions built around the next debate’s format, a town-hall-style meeting, where Trump is likely to engage with undecided voters asking him questions and, at times, move from his chair to walk the stage. Trump has little experience with the format, which can be challenging for people who do not practice managing their body language and movements.

Several advisers also want to impress upon him the need to stick to a strategy and a plan of battle against a female candidate — the kind of opponent he has less experience facing — rather than spend time polishing a string of disparate zingers that Clinton, a skilled debater, was able to easily parry Monday night.

Clinton succeeded several times in baiting Trump, making him become defensive, lose his cool or dig himself into a political hole, particularly late in the debate as he struggled to defend himself against charges that he had made sexist and racist remarks. He also repeatedly interrupted or talked over Clinton, which some female voters found alienating. Some allies of Trump say he is not preparing enough to do battle with a woman in mind; he has only one senior adviser who is a woman, his campaign manager, Kellyanne Conway.

Almost all of his advisers rejected the idea that the debate was a failure for Trump, noting that he landed some punches and insisting that Clinton looked more polished than she was because of her opposition.

But all of them described the debate as filled with missed opportunities. And they openly expressed frustration that Trump seemed unable to stop chasing chum that Clinton tossed at him.

Trump’s debate preparation was unconventional. Aides have introduced a podium and encouraged him to participate in mock debates, but he has not embraced them, focusing mostly on conversations and discussions with advisers.

During the primaries, the group briefing him for debates was small and closely held. By the weekend before the debate Monday at Hofstra University, there were nearly a dozen people preparing Trump, including retired Army generals Michael Flynn and Keith Kellogg, neither of whom has experience in presidential debates.

There were early efforts to run a more standard form of general election debate-prep camp, led by Roger Ailes, the ousted Fox News chief, at Trump’s golf course in Bedminster, New Jersey. But Trump found it hard to focus during those meetings, according to multiple people briefed on the process who requested anonymity to discuss internal deliberations. That left Ailes, who at the time was deeply distracted by his removal from Fox and the news media reports surrounding it, discussing his own problems as well as recounting political war stories, according to two people present for the sessions.

Rudolph W. Giuliani, the former New York City mayor and a friend of Trump’s who has been traveling with him extensively, took over much of the preparation efforts by the end. But with Trump receiving so much conflicting advice in those sessions, he absorbed little of it.

The team had primed Trump to look for roughly a dozen key phrases and expressions Clinton uses when she is uncertain or uncomfortable, but he did not seem to pay attention during the practice sessions, one aide said, and failed to home in on her vulnerabilities during the debate.

“It clearly looked like he ran out of gas after 30 minutes, and that came through loud and clear,” said Scott Reed, the senior political strategist for the U.S. Chamber of Commerce, who has not supported Trump.

“Trump needs to show a higher level seriousness, so that he’s better positioned as an agent of change,” Reed added. “If he can accomplish that, he’ll win undecided voters and late-breaking voters who clearly don’t want to support Hillary Clinton.”

Trump’s best lines, several aides said, came when he talked about how Clinton had been in politics for 30 years and had yet to offer any solutions, and when he parried a question from her about releasing his tax returns by saying he would release them when she released the 33,000 deleted emails from her time as secretary of state. But he quickly dropped the emails line.

The aides were particularly frustrated when Trump, unprompted, mentioned comedian Rosie O’Donnell during an exchange about his treatment of women, saying she deserved his vitriol and criticism.

Trump’s campaign tried to soothe supporters on a conference call Tuesday by pointing to instant polls that showed him winning the debate, even though a vast majority of surveys showed that Clinton led. And his backers painted an optimistic picture of a campaign on course.

“I think he was extremely effective in speaking to the targeted audience of swing state voters and undecided voters,” said John Jay LaValle, the chairman of the Republican Party in Suffolk County, N.Y., and a supporter of Trump.

© 2016 The New York Times Company