Donald J. Trump long ago decided he wanted a very different Republican Party platform in 2024. The delegates who arrived in Milwaukee early last week before the Republican National Convention, with grand plans of drafting a sweeping document of party principles, quickly found out just how determined he was.

Within minutes of their arrival, their cellphones were confiscated and placed in magnetically sealed pouches. There would be no leaks of information. It was only then that the delegates received a copy of the platform language the Trump team had meticulously prepared, which slashed the platform size by nearly three-quarters.

“This is something that ultimately you’ll pass,” Mr. Trump told the delegates by phone and made audible to the room, according to a person who was there and who was not authorized to speak publicly. “You’ll pass it quickly.”

He was right. Within hours, the platform committee had endorsed a document that Mr. Trump had personally dictated parts of, according to two people with direct knowledge of the events, and it all happened before the delegates got their phones back.

The committee passed the platform by a vote of 84 to 18.

The new platform softened language on abortion, excised old language referring obliquely to gay conversion therapy and culled a section about reducing a national debt that Mr. Trump had increased by nearly $8 trillion during his term in office. But the most revealing part was not any particular provision or plank.

It was the ruthless efficiency of a process months in the making that squelched, silenced or steamrolled any forces who might oppose Mr. Trump. The result was the latest evidence of the political maturation of Mr. Trump and his operation.

The first years of Mr. Trump’s presidency were defined by obstruction. He was repeatedly redirected by advisers and rebuffed on Capitol Hill. But now, as he is about to formally accept the Republican Party’s nomination on Thursday in Milwaukee for the third consecutive campaign, Mr. Trump is a political veteran who has spent nearly 10 years grinding down his opposition, purging those who are disloyal and remaking the party in his image.

President Biden and his advisers have made the specter of a second Trump term central to their campaign to defeat him, warning that his talk about the “termination” of the Constitution and of political “retribution” is a threat to American democracy. The critical rhetoric was briefly tamped down after Mr. Trump survived an attempt on his life on Saturday by a 20-year-old gunman.

But the official G.O.P. platform — and the way the Trump team muscled it through the party structure — foreshadows much beyond the words on the pages. It showcases a candidate who is increasingly confident of his own vision and who has surrounded himself with a team that knows both the rules and how to bend them.

And if he retakes the White House, the platform push may be a blueprint for how Mr. Trump might govern, aided by a pliant Republican Party and abetted by a federal judiciary that he himself reshaped during his first term.

“What it says is that the Republican Party is Donald Trump’s party,” Chris LaCivita, one of Mr. Trump’s top campaign aides, said in an interview. “Donald Trump has put the imprint, quite frankly, that he should have had in 2016 and 2020 on the party as a whole in 2024.”

Shorter, Simpler and More Vague

In 2020, Mr. Trump’s advisers, including his son-in-law Jared Kushner, wanted to cut the Republican platform down to one page of principles. It would have been a simple way of entirely removing controversial topics that might prove politically unpopular, such as staunch opposition to same-sex marriage and an allusion to the party’s preference for permitting parents to choose gay conversion therapy for their children. The idea went nowhere.

Too many people had a stake in the platform, and getting Mr. Trump a pared-down document would have caused too fierce a clash inside the party, his advisers concluded. So the Trump team backed off. Citing challenges posed by the coronavirus pandemic, the Trump team ultimately did not have a new platform at all; the 2020 version simply reproduced the 2016 platform — a 66-page document that included many policies that Mr. Trump did not personally agree with.

Mr. Trump made clear to his team that he wanted the 2024 platform to be his and his alone. He wanted it to be much shorter and simpler — and, in some cases, vaguer. He was especially focused on the language about abortion, which he recognized was a potentially potent issue against him in a general election. He wanted nothing in the platform that would give Democrats an opening to attack him, and he made clear to aides that he was perfectly fine with bucking social conservatives, for whom he had delivered a tremendous victory by reshaping the Supreme Court with a conservative supermajority.

Mr. Trump also stressed that he did not want to define marriage as between one man and one woman. Instead, the document contains a vague statement open to interpretation: “Republicans will promote a Culture that values the Sanctity of Marriage.”

One person involved in the process recalled Mr. Trump saying privately: “Sanctity of marriage. Don’t define it.”

Three months ago, Mr. Trump’s team set about giving him the platform he wanted.

The Trump campaign decided it would go to every delegation in the country to handpick the people who would represent the campaign on committees for rules, credentials and the party platform. It was an enormous organizational exercise overseen by Mr. Trump’s senior adviser James Blair.

A small team was set to draft the platform. A speechwriter, Vince Haley, took the lead. There were only a handful of people on a list of those receiving the text, according to a person involved in the process who was not authorized to discuss the details publicly.

The team of Trump advisers had sessions where the platform was printed out and they would sit around the table at Mar-a-Lago and campaign headquarters in Palm Beach, Fla., to review the language. The group included Mr. Haley; Mr. Blair; Mr. LaCivita; Mr. Trump’s strategist and pollster, Tony Fabrizio; another speechwriter, Ross Worthington; and Mr. Trump’s top political adviser, Susie Wiles.

The first draft came in around 8,000 words, according to two people involved. Then it was slashed to around 5,000. The final document was less than half the length of the original.

The platform reads in part like a Trump campaign speech, with the former president’s idiosyncratic syntax and random capitalization throughout. Mr. Trump himself dictated edits over the phone, including on a late-night phone call in the final days that resulted in a doubling of the number of party principles from 10 to 20, according to a person with direct knowledge of the process.

A Process That Felt ‘Hostile’

Platform day arrived last Monday. Party regulars arrived in Milwaukee with a sense of excitement. Many of these activists look forward every four years to shaping the Republican Party’s official vision, and they pay their own way to participate in the process.

Members of the platform committee arrived expecting two days of work ahead, prepared to break into subcommittees to draft sections of a document that typically spans thousands of words.

Instead, they handed over their phones to party officials, who sealed them in the magnetic pouches. Mr. Trump and party operatives were allowed to keep their devices. Only delegates and guests were denied the ability to communicate with the outside world.

Senator Marsha Blackburn of Tennessee, one of Mr. Trump’s staunchest allies in the Senate, presided over the meeting. It became clear very quickly to those who wanted to amend the platform that Mr. Trump’s team controlled the room.

One delegate, a state lawmaker from Arizona, Alex Kolodin, had brought a laptop and printer to be prepared. But there was a quick vote to confiscate those — and any other electronics.

“The will of the body is the will of the body,” Mr. Kolodin said of having his devices taken.

Mr. Kolodin said he had submitted ideas to the Trump team before the platform committee meeting but did not realize those gathered would have no actual say in the final document.

“This is all for show,” Mr. Kolodin said, adding that he wished the party had shared that fact in advance. “We all would have felt more respected by that upfront approach,” he said.

Gayle Ruzicka, who has been attending conventions since 1992 and served on multiple platform committees, said the participants had been told the evening before that there would be subcommittee meetings. Instead, she said, delegates were handed what they were told was a draft on Monday. She said that after roughly two hours and no amendments considered, the draft was ratified in full.

“It was not honest, and that was what bothered me,” Ms. Ruzicka said.

There were roughly two hours of speeches but little to no debate about specific platform provisions, she said, adding, “We ended up voting on the platform we hadn’t even read yet.”

But Ms. Ruzicka, among the social conservatives hoping to offer stronger anti-abortion language, did not blame Mr. Trump. “I don’t think he told his people to lie to us,” she said.

Tabitha Walter, the executive director of the Eagle Forum, a conservative group that focuses on social issues, was a credentialed guest but said that party officials closely shadowed her, with one person seemingly assigned to her individually.

“Anywhere I would go get coffee and go to the bathroom, she would follow me around,” Ms. Walter said. “Any time I would take notes, she would read them.” She added that it “felt very hostile,” calling the platform experience a “strong-arming.”

Suzi Voyles, a Georgia platform delegate, also wanted a firmer stance on abortion and was disappointed to have only two hours — and little say in the platform.

“A draft,” she said, “should not become the final document.”

Mr. LaCivita maintained in an interview that Mr. Trump “has proven his credentials on the issues of import to evangelical voters and otherwise” through his record in office.

Ms. Voyles conceded that Mr. Trump had learned a lot about how to operate the inside game.

“They did a marvelous job on what might be called a whip team,” she said of the Trump vote-counting operation. “He better understands how to effectively accomplish getting from Point A to Point B.”