MANCHESTER, N.H. — Florida Gov. Ron DeSantis on Sunday ended his once-promising presidential campaign, which steadily deflated as he struggled to connect with voters and convince Republicans to swap Donald Trump for a younger, more disciplined champion of his ideas.

As he departed the contest, DeSantis endorsed Trump, who had relentlessly attacked the Florida governor with demeaning nicknames and charges that he was disloyal. His exit came just two days before voting in New Hampshire’s primary, where Trump appears to be closing in on another victory that would underscore his unrivaled grip on the GOP.

DeSantis, 45, had seemed to many Republicans like the most viable challenger to Trump after the 2022 midterms, when the governor won reelection by a landslide. But he started to lose ground in polling even before his official campaign launch in May — via a glitchy live chat that neatly embodied the way his grand plans were going awry.

“It’s clear to me that a majority of Republican primary voters want to give Donald Trump another chance,” DeSantis said in a video message he posted Sunday afternoon on the social media site X, formerly known as Twitter. “They watched his presidency get stymied by relentless resistance, and they see Democrats using lawfare to this day to attack him.”

He acknowledged “disagreements” with Trump — he spent the past year effectively calling Trump self-absorbed and ineffective — but suggested Trump’s remaining GOP rival, Nikki Haley, was worse. “We can’t go back to the old Republican guard of yesteryear, a repackaged form of warmed-over corporatism that Nikki Haley represents,” DeSantis said.

Even before DeSantis dropped out, Haley had emerged as the most viable challenger to Trump, polling closer to him in New Hampshire, where independents and moderate Republicans have given her a particular boost. But it’s not clear that she can pull off an upset, and she faces a tough road ahead. On Sunday she said DeSantis “ran a great race” and has “been a good governor.”

“Having said that, it’s now one fella and one lady left,” said Haley, a former U.N. ambassador and former South Carolina governor.

Trump’s campaign said in a statement it was “honored” by DeSantis’s endorsement and said “it is now time for all Republicans to rally behind President Trump” against Biden.

DeSantis echoed Trump’s combative style and “America First” rallying cry while arguing he would be more electable, truer to conservative values and more effective at executing an agenda. He appealed heavily to the party base as someone willing to dig in on polarizing issues and go to battle with critics, the media and companies such as Disney. Struggling to make headway against Trump, he increasingly criticized the former president as “high risk” and “low reward” for the Republican Party.

But the second-term governor’s strategy fell flat as voters refused to leave Trump and even gravitated back to him, galvanized by outrage at the former president’s four criminal indictments. DeSantis alienated more moderate primary voters and donors who increasingly looked to Haley as a Trump alternative. Awkward interactions on the trail dogged DeSantis’s campaign, spawning viral videos and feeding his longtime reputation for aloofness.

A person deeply involved in DeSantis’s campaign, who, like others, spoke on the condition of anonymity in order to speak freely, said the campaign had a host of problems: no coherent message, warring advisers and a weak small-dollar donor program. DeSantis disliked courting donors and activists, this person said, and spent too much time on culture war issues. When he made adjustments, this person said, it was too late.

“At the end of the day, I don’t think any of it mattered with all the Trump indictments,” this person said. “It wasn’t a well-run campaign, but I don’t think the best-run campaign would have beaten Trump.”

DeSantis barely bested Haley for a distant second in Iowa, the state where he bet the vast majority of his time and resources. After Iowa, DeSantis confronted a difficult map with no obvious states to help him turn the tide.

And a sprawling operation that quickly amassed more than $100 million was plagued by infighting and distrust among different factions. DeSantis loyalists in Tallahassee clashed with the national consultants brought in to run a supportive super PAC — their tensions culminating in the late creation of a new group and the resignations and firings of top officials.

Discussions about dropping out began last week as DeSantis’s team insisted he was staying in and turning his sights to South Carolina. The governor had told donors and allies he had enough money to get through South Carolina, whose GOP primary is Feb. 24, but senior staffers did not see a path to victory, according to a person familiar with the conversations. DeSantis was on track to post a single-digit percentage showing in New Hampshire, polls showed, which could have made his exit more embarrassing.

Most of DeSantis’s senior staff wanted him to drop out of the race, according to a longtime ally of DeSantis who talks to him regularly, who said the governor heard arguments that losses could further damage his brand. DeSantis is determined to still have a future in Republican politics, this person said, and didn’t want to be further damaged for 2028.

The Florida governor said he was resigned to the fact that Republican voters wanted to back Trump — and conservative news outlets and influencers were now against him. DeSantis told one adviser last week that he understood he would probably lose but was not ready to pull the cord.

“He wasn’t going to even break single digits in New Hampshire and had no path in South Carolina,” said a person close to the governor. “He was trying to tell everyone he was just going to hang out and wait for Trump’s legal challenges to play out but that wasn’t feasible and he knew it.”

DeSantis returned to Tallahassee this weekend instead of campaigning in South Carolina through Sunday, as had been planned, according to several people familiar with his travel. His campaign had recently added a Sunday evening event in New Hampshire and tried to bat away speculation the end was near after the governor canceled morning TV appearances.

A GOP star for his strident opposition to coronavirus restrictions in Florida, DeSantis enacted an aggressive home-state agenda in the run-up to his campaign. He passed laws limiting discussion of LGBTQ issues in school, defunding college “diversity, equity and inclusion” programs and banning abortion after roughly six weeks of pregnancy, among many others. He called Florida “the place where woke goes to die,” touting the GOP’s dominance in the state and his nearly 20-point margin of victory in 2022, which led the New York Post to nickname the governor “DeFuture.”

Despite the national buzz, some Republicans who worked with DeSantis in Florida harbored doubts that his success in the state would translate on a national stage. As governor, they said, DeSantis was effective but ruthless and insular, unenthusiastic about the social aspects of politics and keeping a small circle of trust that centered on his wife. Replacing his campaign manager in August, DeSantis chose a loyal aide from the governor’s office without campaign experience — a shake-up that one fundraiser panned as “rearranging deck chairs on the Titanic.”

Money was one of DeSantis’s big advantages when he entered the race. His campaign raised a formidable $8 million within 24 hours of launching. And more than $80 million left over from his gubernatorial reelection was transferred to his primary super PAC, Never Back Down, which took on many functions traditionally handled by campaigns and pushed the limits of legal restrictions on such an outside group’s ability to coordinate with their favored candidate. Never Back Down built a massive door-knocking program, took on some of his private plane costs and hosted many of DeSantis’s events, inviting him as a “special guest.”

But the campaign quickly ran into financial trouble after launching with a massive staff and setting expectations for fundraising too high. Layoffs commenced. The super PAC absorbed even more costs. Major donors were also backing away, some of them aghast at DeSantis’s signing of a six-week abortion ban or his statement to then-Fox host Tucker Carlson that the U.S. had no compelling reason to become “further entangled in a territorial dispute between Russia and Ukraine.”

Billionaire Ken Griffin, a top funder of DeSantis’s gubernatorial reelection, was initially expected to make a major contribution to the DeSantis effort. But he grew critical of the governor. The largest known contributor to Never Back Down, businessman Robert Bigelow, pulled back and said in August that DeSantis had gone too far to the right. Griffin was most angry about DeSantis’s position on abortion, and multiple entreaties from DeSantis advisers could not win his support for the governor, according to people familiar with the situation. Wall Street leaders close to him then gave to Haley.

Trump’s indictments — starting in late March — marked the start of a polling decline for DeSantis with voters who approve of the former president. In polling and focus groups, DeSantis backers and other Republicans found that many seemingly logical lines of attack on Trump were ineffective.

Still, DeSantis eventually ramped up his criticism of Trump, a former ally whose endorsement once helped DeSantis beat the establishment candidate in Florida’s 2018 gubernatorial race. He used the second GOP debate in September to assail Trump’s absence, calling him “missing in action.” On the trail, he lamented that “Trump views everything through the lens of him.”

DeSantis banked on a strong performance in Iowa, the first state in the GOP nominating calendar. He had championed causes important to the evangelical voters who dominate the Republican caucuses there, and tapped into the Christian social conservative networks that powered past winners in the Hawkeye State. His legislative priorities in Florida echoed the priorities of Iowa Republicans, who also passed a six-week abortion ban that got caught up in the courts.

Trump, meanwhile, had attacked prominent conservatives in the state, including Gov. Kim Reynolds (R). Reynolds, who grew deeply frustrated with Trump, initially said she was staying neutral but then took the unusual step of endorsing DeSantis in November.

“We need a leader who is looking forward and not backwards,” Reynolds said at the November opening of a DeSantis campaign office near Des Moines. “We need a leader who will follow through on his promises and has a record of following through on his promises.” The phrase “no excuses” became a sort of unofficial campaign slogan as DeSantis leaned into the idea that he could get things done where others, particularly Trump, had fallen short.

DeSantis fulfilled his early pledge to campaign in all of Iowa’s 99 counties, racked up legislative endorsements and moved much of his campaign staff there in the fall. Yet Trump maintained a large lead in Iowa and everywhere else.

“DeSantis would make the best president,” said DeSantis donor and surrogate Dan Eberhart. “Unfortunately, he didn’t run the best campaign.”

As DeSantis struggled, the divisions in his team grew and spilled out into public view. Close allies of the governor launched a new super PAC late in the fall, and campaign leadership gave the new organization its blessing to effectively take over advertising. Sidelined and instructed to focus on field organizing, Never Back Down saw repeated shake-ups in leadership.

Its CEO resigned. His replacement was fired less than two weeks later, along with two other senior officials, and the chairman of the group’s board — former Nevada attorney general Adam Laxalt, a longtime friend of DeSantis’s — left, too. Scott Wagner, a Florida-based lawyer and college friend of the governor, took the helm and accused the fired officials of misconduct, prompting the group’s chief strategist Jeff Roe to join the exodus with a month to go before the Iowa caucuses. Roe alluded to Wagner’s comments and said they were false.

Trump’s team had taken particular delight in criticizing DeSantis — many of Trump’s former advisers had worked for the governor before falling out with him, and his team had a universal dislike for Roe.

For example, DeSantis had fired Susie Wiles, once his top aide, after he became governor in 2019 — and sought to convince others to fire her as well, including Trump, the lobbying firm where she worked and the RNC.

In 2021, she took helm of Trump’s operation when the former president was at the nadir of his political influence in the GOP and has spent the last three years working to make him the GOP nominee. Late Saturday, as DeSantis canceled his events for Sunday, Wiles posted a two-word tweet, her first in months.

“Bye bye,” she wrote.

Dylan Wells contributed to this report.