Trump takes Iowa, and a big first step toward a rematch with Biden.

Donald J. Trump won the Iowa caucuses on Monday, a crucial first step in his bid to reclaim the Republican nomination for the third consecutive election as voters braved the bitter cold, looked past his mounting legal jeopardy and embraced his vision of vengeful disruption.

The victory, called by The Associated Press on Monday night only 31 minutes after the caucuses had begun, accelerated Mr. Trump’s momentum toward a historic potential rematch in November with President Biden that could play out on both the campaign trail and in the courtroom.

In a state that had rejected him in the caucuses eight years ago, Mr. Trump finished ahead of two of his main rivals, Ron DeSantis and Nikki Haley, both of whom were locked in a race for second place. It was unclear who had won second and who had won third.

The result was a setback for both Republicans, who had spent as much time and money battling each other in Iowa as the front-runner. Mr. DeSantis, the Florida governor, had previously predicted victory in Iowa, and both he and Ms. Haley, the former United Nations ambassador, have argued that a strong second-place finish would better position them as Mr. Trump’s chief rival going forward.

Mr. Trump is the first former president in the modern era who has sought to return to the White House. On Monday, he was hoping to shatter the Republican record for the largest victory ever in a contested caucus, which was just under 13 percentage points. Despite the quick declaration of Mr. Trump as the winner, it was not yet clear if he would win an outright majority of more than 50 percent, a critical psychological barrier for those in the party still hoping to stop him.

A spokesman for Mr. DeSantis, Andrew Romeo, said in a statement that the early declaration of Mr. Trump’s victory was “absolutely outrageous.” He borrowed a phrase from Mr. Trump to accuse the media of participating “in election interference by calling the race before tens of thousands of Iowans even had a chance to vote.”

Regardless of what comes next, Mr. Trump’s Iowa victory amounts to a remarkable resurrection of a political career that had once appeared in tatters. He was impeached in the final days of his first White House term for his role in inciting the Jan. 6, 2021, riot at the Capitol. His subsequent acquittal by the Senate left open the possibility of this return campaign.

Mr. Trump has spent the last three years methodically consolidating power to ready his own restoration. Even his four felony indictments, and his status as the only former American president to ever face criminal charges, have united many Republicans behind his claims of “election interference” and victimhood at the hands of Democrats and the “deep state.”

Now, the Republican calendar will turn to New Hampshire, where polling shows Mr. Trump is expected to face a strong challenge from Ms. Haley in a state where independent voters can also cast ballots. Mr. Trump’s campaign and allied super PAC have already been blanketing that state with anti-Haley advertising, a sign of its competitiveness ahead of the Jan. 23 primary.

Mr. DeSantis had entered 2023 as the party’s clear alternative to Mr. Trump. But early struggles, both financially and electorally, forced him to retrench and make his stand in Iowa, where he won the backing of the state’s popular Republican governor and a key evangelical network. His super PAC knocked on more than 935,000 doors statewide.

Even with Mr. Trump far ahead, Ms. Haley’s allied super PAC spent more than $22 million on attacks against Mr. DeSantis just in Iowa, hoping to squash his candidacy in the very first state (the group had spent nothing opposing Mr. Trump in Iowa, according to federal records). Heading into the caucuses, Mr. DeSantis had pledged to run a “long” and “scrappy” campaign regardless of the result and symbolically decided to fly directly to South Carolina after Iowa instead of to New Hampshire, a state where he has been polling in the single digits.

Mr. Trump’s team believes a string of early victories — first in Iowa, then in New Hampshire, Nevada and South Carolina — will position him for a blowout on Super Tuesday, all but locking up the nomination by March, when many of the delegates are up for grabs. But they worry an early loss could lead to a more protracted fight.

In Iowa, harsh winter conditions had scrambled turnout expectations and preparations for all the campaigns in recent days. First, a blizzard forced a slew of event cancellations. Then, subzero temperatures and a numbing windchill on Monday spurred warnings of “life-threatening cold” from the National Weather Service.

But supporters of Mr. Trump, who describes his followers as part of a broader “MAGA movement,” nonetheless turned out, animated by his dark portrait of a nation in decline and apocalyptic rhetoric about wresting a country controlled by the left back from the brink. Mr. Trump’s vows to exact retribution on his political enemies have earned warnings from academics and Democrats of a drift toward authoritarianism yet have won cheers from his rapturous crowds.

In many ways, Mr. Trump’s victory represented a repudiation of the rituals of campaigning in Iowa, a state that has previously rewarded candidates who expose themselves to up-close scrutiny, submit themselves to tough questioning or who visit each of the state’s 99 counties, as Mr. DeSantis did.

Mr. Trump did little of that, visiting only a fraction of the state’s counties and appearing at only a single in-person rally in the final week of the campaign, citing icy conditions for some cancellations. He did indulge in some traditions — stopping by a Casey’s gas station to pick up pizza that he then delivered to firefighters this weekend. But more often, he leveraged his unique status as a former president to travel in a Secret Service motorcade and command national attention from anywhere, including a courtroom appearance and news conference in New York in the last week.

His approach reflected the increasing nationalization of American politics, where cable news appearances are often as persuasive as meet-and-greets in small towns. Still, Mr. Trump, remembering bitterly how his lack of political organization had damaged him in the 2016 caucuses, invested early and heavily in the state, building out a robust staff and recruiting more than 1,800 people as “caucus captains” for the more than 1,600 precincts in the state.

Among Mr. Trump’s most meaningful decisions was his refusal to even debate his rivals.

His absence from the primary’s most-watched moments forced his rivals to fight one another and robbed them of any opportunity to dent his lead. And so while Iowa has traditionally played a key role in winnowing the field, that occurred this cycle before the balloting even began. Former Vice President Mike Pence, Senator Tim Scott and former Gov. Chris Christie all bowed out after failing to gain any significant traction. Another former Republican rival, Gov. Doug Burgum of North Dakota, endorsed Mr. Trump on Sunday.

Vivek Ramaswamy, an entrepreneur who has heavily funded his own run and who has spoken mostly positively about Mr. Trump while traveling exhaustively across Iowa, struggled to pick up momentum. After something of a truce for most of the campaign, Mr. Trump and his advisers laced into Mr. Ramaswamy in the last two days before the caucuses, with the former president’s team seeing him as siphoning off potential votes.

Long before the caucuses, Mr. Biden had begun to center his re-election bid on casting Mr. Trump as an existential threat to American democracy, citing his predecessor’s refusal to accept the results of the last election and his impeding of the peaceful transfer of power in 2020.

A special counsel appointed by the Justice Department, Jack Smith, has indicted Mr. Trump over his role in that postelection period to subvert the will of the people. The case could go to trial in 2024 — before the general election.

The election subversion case is only one of four indictments that Mr. Trump faced in 2023, along with charges that cover his handling of classified documents, his hush-money payments to an adult film actress in his 2016 campaign and his attempts to reverse the 2020 election results in Georgia.

If Mr. Trump does become the nominee, the 2024 campaign will have few modern parallels.

He is poised to split his time between the campaign trail and his criminal as well as other civil cases. And soon, the Supreme Court is expected to weigh in on the basic question of whether states can outright ban Mr. Trump from the ballot over his role in the Jan. 6 riot. A different case making its way through the federal courts will test Mr. Trump’s claim that he should be immune from prosecution.

Ms. Haley has made the uncertainty and turbulence that nominating Mr. Trump would bring to the contest a central part of her pitch. “Chaos,” she has said, “follows him.”