The reality has been clear for weeks, since former President Donald J. Trump trounced his opponents across the frozen fields and icy highways of Iowa. But his overwhelming victory on Saturday in South Carolina, where he defeated Nikki Haley in her home state, makes it all but official.

The Republican nominating contest isn’t a competition. It’s a coronation.

The party primaries this winter represented the best chance for Republicans who were opposed to the former president to oust him from his dominant position in the G.O.P. The stakes were extraordinarily high: Many of his Republican opponents see Mr. Trump as, at best, unelectable and, at worst, a threat to the foundations of American democracy.

And yet, as the campaign has moved through the first nominating contests, the race has not revealed Mr. Trump’s weaknesses, but instead the enduring nature of his ironclad grip on the Republican Party. From the backrooms of Capitol Hill to the town hall meetings of New Hampshire to the courtrooms of New York City, Mr. Trump shows no sign of being shaken from his controlling position in the party — not in 2024, and not in the foreseeable future.

“I think the party will be done with Trump when Trump is done with the party,” said David Kochel, a longtime Republican strategist who is opposed to Mr. Trump. “That’s the long and short of it.”

All of Mr. Trump’s primary rivals, except Ms. Haley, have folded and endorsed his candidacy. He has conquered state parties and the Republican National Committee, installing loyalists in key posts, and collected the backing of vast numbers of Republican elected officials. And what once appeared to be extraordinary political liabilities — the 91 felony counts against him, his increasingly extreme rhetoric, his role in the Jan. 6 riot at the Capitol — have only served to bolster his support among the Republican faithful.

With his victory on Saturday, Mr. Trump has swept all the early nominating contests — Iowa, New Hampshire, Nevada, the U.S. Virgin Islands, South Carolina — an unprecedented achievement in a contested primary race. He heads into Super Tuesday on March 5, when a third of all delegates to the G.O.P. convention will be awarded, with “maximum velocity,” said the Republican governor of South Carolina, Henry McMaster, who endorsed Mr. Trump over his predecessor, Ms. Haley.

Ms. Haley has vowed to remain in the race, scheduling events in the coming days in Michigan, Minnesota, Colorado and Utah. On Saturday night, she argued that broad swaths of the Republican primary electorate still wanted an alternative to Mr. Trump.

“They have the right to a real choice, not a Soviet-style election with only one candidate,” she told supporters at her election night party. “And I have a duty to give them that choice.”

Ms. Haley has a point: In Iowa and New Hampshire, Mr. Trump won with about half of the vote, indicating that his support may have a ceiling even within his own party. In exit polls and surveys, Haley backers expressed negative views about Mr. Trump, indicating that a faction of the Republican coalition has concerns about the former president.

But those Trump skeptics are not a majority of the party. Nor have they been enough for Ms. Haley to win a primary race, leaving her running a campaign that many Republican strategists and officials believe is headed toward inevitable defeat.

“This is the fastest primary process since I can remember,” said Ron Kaufman, a Republican presidential strategist who has been involved in primary campaigns since Ronald Reagan ran in 1976. “There isn’t anyone who doesn’t perceive Trump being the nominee, including Nikki Haley. Whether you like it or don’t like it, everyone understands he is the perceived nominee.”

Barring a spring surprise — a debilitating health issue, a legal event — Mr. Trump appears to be on a rapid march to the Republican nomination. It’s a reality that shows how Mr. Trump has driven his party — and the nation — into a new era where once-unthinkable policies and rhetoric have become standard. Mr. Trump has floated breaking from NATO, conducting mass deportations and prosecuting his political enemies.

But between his promises to not be a dictator “other than Day 1” and to dismantle core elements of American governance, democracy and the rule of law, Republicans not only have stood by the former president but have rewarded him with electoral victories.

“The power of Trump in the Republican Party is extraordinary — he causes people to defy common sense,” said Gov. Roy Cooper of North Carolina, a Democrat. “It’s stunning.”

Republican opponents of Mr. Trump insisted he could be defeated if the race narrowed to a one-on-one contest. The mistake of 2016, they argued, was that his rivals remained in the race too long, allowing him to win with a plurality by splitting the votes against him.

This year, several of Mr. Trump’s rivals folded before voting began. Gov. Ron DeSantis of Florida, once seen as his strongest opposition, ended his campaign humiliated.

That left Ms. Haley as Mr. Trump’s only competition and created the man-versus-woman contest his opponents had long hoped to see. In the final days of the South Carolina race, she escalated her attacks on the former president — following what Trump opponents, including former Gov. Chris Christie of New Jersey, had believed was the strategy that could defeat him.

Yet, she failed to win in New Hampshire, perhaps the most favorable terrain in her bid, given the large presence of independent voters and moderate Republicans who participate in the party primary. In the Nevada primary, where Mr. Trump didn’t compete, she was defeated by “none of these candidates.”

Her loss in South Carolina was particularly damaging, as it came from voters who knew her better than perhaps anywhere else in the country. Her home state rejected her by a double-digit margin. She appeared to win only a handful of counties in the state, all home to larger numbers of moderate white college-educated independents.

Mr. Trump’s dominance is not limited to the campaign trail. On Saturday, at the Conservative Political Action Conference, a straw poll of Mr. Trump’s potential vice-presidential picks overshadowed the one about the presidential nomination — a survey Mr. Trump won with 94 percent.

On Capitol Hill, earlier this month, Mr. Trump opposed long-awaited border legislation, and Senator Mitch McConnell, Republican of Kentucky and the minority leader, changed course and tanked the bill.

And even Mr. Trump’s most inflammatory statements no longer draw even the mild rebukes from within his party that they once did during his presidency. Many of those critics have resigned, retired or been driven to political defeats with help from Mr. Trump.

When the former president compared his criminal indictments to the situation of the Russian opposition leader Aleksei A. Navalny, who died in prison, Republicans offered no response.

When Mr. Trump suggested he had threatened to encourage Russia to do “whatever the hell they want” to a NATO ally that failed to meet its financial commitments, European leaders reacted with alarm and public rebukes. Republicans shrugged.

Nor did they reject Mr. Trump’s comments at CPAC on Saturday attacking his political adversaries in strident terms and casting himself — a former president and the figurehead of his party — as a “political dissident.”

“I stand before you today, not only as your past and hopefully future president, but as a proud political dissident,” he said. “I am a dissident.”

Some who have opposed Mr. Trump have spent recent days trying to find reasons for his seeming invincibility.

On a private call leaked to reporters, Mr. DeSantis suggested to supporters of his campaign that conservative media outlets were responsible for Mr. Trump’s support, saying they provided “no accountability” of the former president.

“He said at some point he could shoot someone on Fifth Avenue and not lose a vote,” Mr. DeSantis said, referring to Mr. Trump. “Well, I think he could shoot someone on Fifth Avenue, and the conservative media wouldn’t even report on it.”

Gov. Chris Sununu of New Hampshire, a moderate Republican who is backing Ms. Haley, said Mr. Trump was sweeping the primaries because of the media coverage of his legal peril and court appearances.

“I said that to the folks at CNN and Fox, you guys keep propping this guy up,” Mr. Sununu said. “You keep highlighting the fact that he’s in court, you keep allowing him to be a victim, and he’s only winning because of the victimization of himself and he loves it. He knows how to play that very, very well.”

The reality may be far more fundamental than media coverage. Despite the political risk, a majority of Republican voters like Mr. Trump. And in this primary contest, that very well could be just enough.