Donald J. Trump’s campaign couldn’t have scripted the results in Iowa any better.

Except for a single vote.

Standing backstage at his victory party in downtown Des Moines, Mr. Trump appeared almost giddy with disbelief as television screens blared the news of an outcome so lopsided it was called while the voting was still underway. He had won more than 50 percent of the vote — and 98 of the state’s 99 counties — and his rivals, Ron DeSantis and Nikki Haley, were clustered together far behind. Mr. DeSantis edged just ahead of Ms. Haley, enough to stall her momentum but not enough to save his candidacy.

“Did you think it was going to be like this?” Mr. Trump remarked to an adviser, according to two people who witnessed the interaction.

That night, the former president and his usual coterie of top aides were joined by about a dozen Iowa staffers headed for New York, boarding the plane his campaign calls Trump Force One.

Not everyone was invited. Mr. Trump had lost Johnson County, home of the University of Iowa, by a single vote. The regional political director who had overseen the area was not given a seat on the plane. The next morning, according to two people familiar with the matter, she was informed by a terse email from her supervisor that her contract with the Trump campaign was not being renewed.

It was the type of ruthlessness the Trump team had deployed in the prior 14 months: Win — or else. The approach has fit the requirements of a candidate who faces the threat of imprisonment if impending trials and the 2024 presidential race do not go his way.

On Tuesday, Mr. Trump beat Ms. Haley by 11 percentage points in New Hampshire, the early state where she had not long ago seemed best situated to score an upset win. His victory came only one week after Mr. DeSantis lost Iowa, his strongest early state, so badly he exited the race.

How Mr. Trump swept the first two states — smoothing his path to the nomination at this early stage — is certainly a tale of cutthroat politics. But that’s only part of the story.

The former president and his allies had luck and a cunning strategy on their side. They put Mr. Trump’s unerring instincts for revving up the Republican base and belittling his opponents to effective use. He benefited from criminal indictments that rallied Republicans around him and a fractured opposition that spent millions of dollars savaging each other instead of him — a replay of the 2016 Republican primaries. Along the way, Mr. Trump consistently evaded ideological labels, along with misguided and mistimed efforts to diminish him.

The Trump team couldn’t believe its luck in October when Ms. Haley’s super PAC began to reserve advertising time attacking Mr. DeSantis.

From the beginning of the campaign, Mr. Trump and his top advisers had seen Mr. DeSantis as their only serious rival. They had spent months savaging him. Ms. Haley had started her campaign with no money and with polling in the single digits. But by fall she was vying with Mr. DeSantis in early-state polls after her August debate performance won positive reviews.

The anti-DeSantis spending from Ms. Haley’s largest super PAC, SFA Fund, kept rising: $1.3 million in October expenditures, $4.4 million in November. It ballooned in December to $15.2 million — with almost all the money going to crush Mr. DeSantis in his must-win state of Iowa.

“Nikki Haley spent millions of dollars on TV attacking Ron DeSantis so we didn’t have to,” said Chris LaCivita, a top campaign adviser to Mr. Trump.

One especially cutting ad from the Haley super PAC repurposed parts of a 2018 commercial from Mr. DeSantis’s primary campaign for governor that featured Mr. DeSantis teaching his children by using Trump slogans and reading from Mr. Trump’s book “The Art of the Deal.” The super PAC’s new anti-DeSantis ad interspersed those 2018 clips with a crowd chanting “Who’s your daddy?”

The ad was a sharp dig at Mr. DeSantis, but not only because of its content: The “Who’s your daddy” ad was produced by Something Else, the same firm that made the original DeSantis ad in 2018. In his career, Mr. DeSantis’s management style has left a long wake of antagonized former aides, including some now at the top ranks of the Trump campaign.

Ms. Haley’s rise also drained Mr. DeSantis’s resources. One of his allied super PACs, Fight Right, spent 25 times as much money, nearly $10 million, attacking Ms. Haley compared with what it spent hitting Mr. Trump, federal records show.

And the money kept coming. On Nov. 28, one of the most financially powerful institutions on the right came to Ms. Haley’s aid. The political network founded by the billionaire industrialist brothers Charles and David Koch endorsed Ms. Haley and began spending millions of dollars to elevate her. It deployed its massive field organization to knock on doors in Iowa and New Hampshire — giving her a ground army she could not have afforded on her own.

But several Koch network donors began raising questions about the decision.

The investor Chart Westcott sent a text message to other Koch donors, describing the endorsement as a “half-baked moonshot,” adding that “outside of Trump being a corpse, there is no path, zero, for Haley to the nomination.”

The circular Republican firing squad — with the bullets aimed at everyone besides the guy who led the race — represented a replay of the 2016 primary campaign. In that race, Mr. Trump’s well-funded rivals spent tens of millions of dollars destroying one another and left Mr. Trump largely unscathed.

“For a second primary cycle, no one laid a glove on Trump with paid media,” Chris Christie, the former governor of New Jersey who dropped out of the presidential race earlier this month, said in a brief interview. Mr. Christie had consistently lashed Mr. Trump on the stump and aired critical ads, but he did not have the resources to fund a significant effort on television.

The one well-funded organization that did try to attack Mr. Trump early through paid media — an offshoot of the Club for Growth, a conservative anti-tax group — quickly concluded that its effort was futile. The group’s leader, David McIntosh, wrote a memo in September that effectively waved the white flag. Nothing had dented Mr. Trump, and tests showed that some ads had even backfired and strengthened Mr. Trump.

A spokeswoman for Ms. Haley, Olivia Perez-Cubas, said in response in an interview that Ms. Haley had begun at 2 percent in a 14-person race and that “in a few months, we cleared the field, raced to 43 percent in New Hampshire and made it a two-person race. We’re just getting started.” She added that Ms. Haley would continue to fight for “the 70 percent of all Americans who don’t want a Biden-Trump rematch.”

Trump advisers were stunned that no lessons had apparently been learned from 2016. Even the two early-state Republican governors determined to defeat Mr. Trump in 2024 found themselves working at cross purposes. Gov. Kim Reynolds of Iowa endorsed Mr. DeSantis. Gov. Chris Sununu of New Hampshire backed Ms. Haley.

Once again, Mr. Trump’s opponents had divided and conquered themselves.