In November, Representative Byron Donalds scored a coveted speaking slot: introducing Gov. Ron DeSantis after a landslide re-election turned the swing state of Florida deep red. Standing onstage at a victory party for Mr. DeSantis in Tampa, Mr. Donalds praised him as “America’s governor.”

By April, Mr. Donalds was seated at a table next to another Florida Republican: Donald J. Trump. He was at Mar-a-Lago, Mr. Trump’s private club, for a multicourse dinner with nine other House Republicans from Florida who had spurned their home-state governor to endorse the former president’s 2024 run. Red “Make America Great Again” hats decorated their place settings.

In six short months from November to May, Mr. DeSantis’s 2024 run has faltered before it has even begun.

Allies have abandoned him. Tales of his icy interpersonal touch have spread. Donors have groused. And a legislative session in Tallahassee designed to burnish his conservative credentials has instead coincided with a drop in the polls.

His decision not to begin any formal campaign until after the Florida legislative session — allowing him to cast himself as a conservative fighter who not only won but actually delivered results — instead opened a window of opportunity for Mr. Trump. The former president filled the void with personal attacks and a heavy rotation of negative advertising from his super PAC. Combined with Mr. DeSantis’s cocooning himself in the right-wing media and the Trump team’s success in outflanking him on several fronts, the governor has lost control of his own national narrative.

Now, as Mr. DeSantis’s Tallahassee-based operation pivots to formally entering the race in the coming weeks, Mr. DeSantis and his allies are retooling for a more aggressive new phase. His staunchest supporters privately acknowledge that Mr. DeSantis needs to recalibrate a political outreach and media strategy that has allowed Mr. Trump to define the race.

Changes are afoot. Mr. DeSantis is building a strong Iowa operation. He has been calling influential Republicans in Iowa and is rolling out a large slate of state legislator endorsements before a weekend trip there.

“He definitely indicated that if he gets in, he will work exceptionally hard — nothing will be below him,” said Bob Vander Plaats, an influential Iowa evangelical leader whom Mr. DeSantis hosted recently for a meal at the governor’s mansion. “I think he understands — I emphasized that Iowa’s a retail politics state. You need to shake people’s hands, look them in the eye.”

Still, his central electability pitch — MAGA without the mess — has been badly bruised.

A book tour that was supposed to have introduced him nationally was marked by missteps that deepened concerns about his readiness for the biggest stage. He took positions on two pressing domestic and international issues — abortion and the war in Ukraine — that generated second-guessing and backlash among some allies and would-be benefactors. And the moves he has made to appeal to the hard right — escalating his feud with Disney, signing a strict six-week abortion ban — have unnerved donors who are worried about the general election.

“I was in the DeSantis camp,” said Andrew Sabin, a metals magnate who gave the Florida governor $50,000 last year. “But he started opening his mouth, and a lot of big donors said his views aren’t tolerable.” He specifically cited abortion and Ukraine.

Three billionaires who are major G.O.P. donors — Steve Wynn, Ike Perlmutter and Thomas Peterffy, a past DeSantis patron who has publicly soured on him — dined recently with Vivek Ramaswamy, the 37-year-old long-shot Republican.

The early months of 2023 have exposed a central challenge for Mr. DeSantis. He needs to stitch together an unwieldy ideological coalition bridging both anti-Trump Republicans and Trump supporters who are nonetheless considering turning the page on the past president. Hitting and hugging Mr. Trump at the same time has bedeviled rivals since Senator Ted Cruz tried to do so in 2016, and Cruz veterans fill key roles in Mr. DeSantis’s campaign and his super PAC.

Allies of both leading Republicans caution that it’s still early.

Mr. DeSantis has more than $100 million stored across various pro-DeSantis accounts. He is building good will with state party leaders by headlining fund-raisers. He remains, in public polls, the most serious rival to Mr. Trump. And a supportive super PAC called Never Back Down is staffing up across more than a dozen states, has already spent more than $10 million on television ads and has peppered early states with direct mail.

DeSantis supporters point to polls showing that the governor remains well-liked by Republicans.

“The hits aren’t working,” said Kristin Davison, chief operating officer of Never Back Down. “His favorability has not changed.”

The DeSantis team declined to provide any comment for this story.

Six months ago, as Republicans were blaming Mr. Trump for the party’s 2022 midterm underperformance, a high-flying Mr. DeSantis made the traditional political decision that he would govern first in early 2023 and campaign second. The rush of conservative priorities that Mr. DeSantis has turned into law in Florida — on guns, immigration, abortion, school vouchers, opposing China — is expected to form the backbone of his campaign.

“Now, the governor can create momentum by spending time publicly touting his endless accomplishments, calling supporters and engaging more publicly to push back on the false narratives his potential competitors are spewing,” said Nick Iarossi, a lobbyist in Florida and a longtime DeSantis supporter.

A turning point this year for Mr. Trump was his Manhattan indictment, which Mr. DeSantis waffled on responding to as the G.O.P. base rallied to Mr. Trump’s defense.

Yet Mr. Trump’s compounding legal woes and potential future indictments could eventually have the opposite effect — exhausting voters, which is Mr. DeSantis’s hope. A jury found Mr. Trump liable this week for sexual abuse and defamation. “When you get all these lawsuits coming at you,” Mr. DeSantis told one associate recently, “it’s just distracting.”

The DeSantis team seemed to buy its own hype.

Days before the midterms, the DeSantis campaign released a video that cast his rise as ordained from on high. “On the eighth day, God looked down on his planned paradise and said, ‘I need a protector,’” a narrator booms as Mr. DeSantis appears onscreen. “So God made a fighter.”

For years, the self-confident Mr. DeSantis has relied on his own instincts and the counsel of his wife, Casey DeSantis, who posted the video, to set his political course, according to past aides and current associates. Mr. DeSantis has been written off before — in his first primary for governor; in his first congressional primary — so both he and his wife have gotten used to tuning out critics.

Today, allies say there are few people around who are willing to tell Mr. DeSantis he’s wrong, even in private.

In late 2022, the thinking was that a decision on 2024 could wait, and Mr. Trump’s midterm hangover would linger. Mr. DeSantis published a book — “I was, you know, kind of a hot commodity,” he said of writing it — that became a best seller. And Mr. DeSantis was on the offensive, tweaking Mr. Trump with a February donor retreat held only miles from Mar-a-Lago that drew Trump contributors.

But it has been Mr. Trump who has consistently one-upped Mr. DeSantis, flying into East Palestine, Ohio, after the rail disaster there, appearing with a larger crowd in the same Iowa city days after Mr. DeSantis and swiping Florida congressional endorsements while Mr. DeSantis traveled to Washington.

One Trump endorser, Representative Lance Gooden of Texas, backed the former president only hours after attending a private group meeting with Mr. DeSantis. In an interview, Mr. Gooden likened Mr. DeSantis’s decision to delay entry until after a legislative session to the example of a past Texas governor, Rick Perry, who did the same a decade ago — and quickly flamed out of the 2012 contest.

“He’s relied, much like Rick Perry did, on local political experts in his home state that just don’t know the presidential landscape,” Mr. Gooden said.

Mr. Trump has insinuated, without providing evidence, that Mr. DeSantis had inappropriate relationships with high school girls during a stint as a teacher in the early 2000s and that Mr. DeSantis might be gay.

His team has portrayed Mr. DeSantis as socially inept, and a pro-Trump super PAC distributed a video — dubbed “Pudding Fingers” — playing off news articles about Mr. DeSantis’s uncouth eating habits.

People close to Mr. Trump have been blunt in private discussions that the hits so far are just the start: If Mr. DeSantis ever appears poised to capture the nomination, the former president will do everything he can to tear him apart.

Beginning with his response to the coronavirus outbreak, Mr. DeSantis’s national rise has been uniquely powered by his ability to make the right enemies: in academia, in the news media, among liberal activists and at the White House. But Mr. Trump’s broadsides and some of his own actions have put Mr. DeSantis crosswise with the right for the first time. It has been a disorienting experience for the DeSantis operation, according to allies.

For the past three years, Mr. DeSantis has had the luxury of completely shutting out what he pejoratively brands the “national regime media” or “the corporate media” — though Rupert Murdoch’s Fox Corporation does not, in his view, count as corporate media.

This strategy served Mr. DeSantis well in Florida. But avoiding sit-down interviews with skeptical journalists has left him out of practice as he prepares for the most intense scrutiny of his career.

“The Murdochs encapsulated him in a bubble and force-fed him to a conservative audience,” said Steve Bannon, a former strategist for Mr. Trump. “He hasn’t been scuffed up. He hasn’t had these questions put in his grill.”

Even in friendly settings, Mr. DeSantis has stumbled. In a February interview with The Times of London, a Murdoch property, Mr. DeSantis cut off questions after the reporter pushed him on how he thought President Biden should handle Ukraine differently.

The former Fox News host Tucker Carlson was so irked by Mr. DeSantis’s evasion that he sent a detailed questionnaire to potential Republican presidential candidates to force them to state their positions on the war, according to two people familiar with his decision.

In a written response, Mr. DeSantis characterized Russia’s invasion as a “territorial dispute.” Republican hawks and some of Mr. DeSantis’s top donors were troubled. In public, the governor soon cleaned up his statement to say Russia had not had “a right” to invade. In private, Mr. DeSantis tried to calm supporters by noting that his statement had not taken a position against aid to Ukraine.

While Mr. DeSantis has stuck to his preferred way of doing things, Mr. Trump has given seats on his plane to reporters from outlets that have published harsh stories about him. And despite having spent years calling CNN “fake news,” Mr. Trump recently attended a CNN town hall.

DeSantis allies said the governor would begrudgingly bring in some of the “national regime media.” Some early proof: The governor’s tight-lipped team invited a Politico columnist to Tallahassee and supplied rare on-the-record access.

Not long after Mr. DeSantis had won in a landslide last fall, the incoming freshman, Representative Cory Mills, a Florida Republican, called the governor’s team to try to thank him for his support. Mr. Mills had campaigned on the eve of the election with Casey DeSantis and had appeared with the governor, too. “I called to show my appreciation and never even got a call back,” Mr. Mills said in an interview. “To be honest with you, I was a bit insulted by it.”

The lack of relationships on Capitol Hill became a public headache in April when Mr. Trump rolled out what eventually became 10 Florida House Republican endorsements during Mr. DeSantis’s trip to Washington.

Donors who contributed to Mr. DeSantis’s previous campaigns tell stories of meetings in which the candidate looked as though he would rather be anywhere else. He fiddled with his phone, showed no interest in his hosts and escaped as quickly as possible. But people who have recently met with Mr. DeSantis say he has been far more engaged. At recent Wisconsin and New Hampshire events, the governor worked the room as he had rarely done before.

The governor and his team have had internal conversations acknowledging the need for him to engage in the basics of political courtship: small talk, handshaking, eye contact.

For his part, Mr. Trump recently relished hosting the Florida House Republicans who had endorsed him.

On one side of him was Mr. Mills. On the other was Mr. Donalds, who had introduced Mr. DeSantis on election night and who had been in Mr. DeSantis’s orbit since helping with debate prep during Mr. DeSantis’s 2018 run for governor.

Mr. Donalds declined an interview. But footage of those private debate-prep sessions, first reported by ABC News, shows Mr. DeSantis trying to formulate an answer to a question that will define his imminent 2024 run: how to disagree with Mr. Trump without appearing disagreeable to Trump supporters.

“I have to frame it in a way,” Mr. DeSantis said then, “that’s not going to piss off all his voters.”