PALM BEACH, Fla. — On any given night, Donald J. Trump will stroll onto the patio at Mar-a-Lago and say a few words from a translucent lectern, welcoming whatever favored candidate is paying him for the privilege of fund-raising there.

“This is a special place,” Mr. Trump said on one such evening in February at his private club. “I used to say ‘ground zero’ but after the World Trade Center we don’t use that term anymore. This is the place where everybody wants to be.”

For 15 months, a parade of supplicants — senators, governors, congressional leaders and Republican strivers of all stripes — have made the trek to pledge their loyalty and pitch their candidacies. Some have hired Mr. Trump’s advisers, hoping to gain an edge in seeking his endorsement. Some have bought ads that ran only on Fox News in South Florida. Some bear gifts; others dish dirt. Almost everyone parrots his lie that the 2020 election was stolen.

Working from a large wooden desk reminiscent of the one he used in the Oval Office, Mr. Trump has transformed Mar-a-Lago’s old bridal suite into a shadow G.O.P. headquarters, amassing more than $120 million — a war chest more than double that of the Republican National Committee itself. Federal records show that his PAC raised more online than the party on every day but two in the last six months of 2021, one of which was Christmas Eve.

And while other past presidents have ceded the political stage, Mr. Trump has done the opposite, aggressively pursuing an agenda of vengeance against Republicans who have wronged him, endorsing more than 140 candidates nationwide and turning the 2022 primaries into a stress test of his continued sway.

Inspiring fear, hoarding cash, doling out favors and seeking to crush rivals, Mr. Trump is behaving not merely as a power broker but as something closer to the head of a 19th-century political machine.

“Party leaders have never played the role that Trump is playing,” said Roger Stone, an on-and-off adviser to Mr. Trump since the 1980s who has been spotted at Mar-a-Lago of late. “Because he can — and he’s not bound by the conventional rules of politics.”

This portrait of Mr. Trump as a modern-day party boss is drawn from more than 50 interviews with Trump advisers past and present, political rivals, Republicans who have sought his support and G.O.P. officials and strategists who are grappling with his influence.

Mr. Trump plainly relishes the power. But as he hints repeatedly about a third White House bid, the looming question is whether he can remain a kingmaker if he doesn’t actually seek the crown.

For now, he has delved into the minutia of cleansing the Republican Party of his critics, even if, in typical fashion, the planning and execution can be haphazard. He has focused his efforts almost obsessively on installing unflinching loyalists in key battleground state posts — governors, senators, House members, secretaries of state and state attorneys general — often in place of the very officials who thwarted his attempts to subvert the 2020 results.

He has pressured candidates to switch the races they enter, counseled Republicans on whom to hire, involved himself in party registration rules in Wyoming and the statehouse speaker’s race in Michigan. He conditioned his endorsement of Gov. Mike Dunleavy of Alaska on Mr. Dunleavy not endorsing the state’s incumbent senator, Lisa Murkowski; Mr. Dunleavy quickly complied. Last week, he issued an anti-endorsement, urging Pennsylvanians to vote for Bill McSwain in the primary for governor, on the grounds that Mr. McSwain had insufficiently embraced his allegations of 2020 election fraud.

Mr. Trump declined to be interviewed for this article.

Those close to Mr. Trump say he draws gratification from the raw exercise of his power. He will listen to the lobbying of senior Republicans, like Representative Kevin McCarthy, the House G.O.P. leader, and then turn on them with little warning. A day after Mr. McCarthy reprimanded Representative Madison Cawthorn of North Carolina for saying that colleagues in Washington had held orgies and used cocaine, Mr. Trump awarded Mr. Cawthorn a coveted speaking slot at his next rally.

‘A developing Tammany situation’

An entire political economy now surrounds Mr. Trump, with Trump properties reaping huge fees: Federal candidates and committees alone have paid nearly $1.3 million to hold events at Mar-a-Lago, records show. A phalanx of Trump whisperers has emerged with candidates paying them in hopes of lining up meetings, ensuring that he sees damaging research on their rivals or strategically slipping him a survey showing a surge in the polls, even as Trump alumni warn that it is always buyer-beware in the Trump influence game.

“If someone is out there selling their ability to make endorsements happen, they’re selling a bridge they don’t own,” said Michael Caputo, a former adviser who still speaks to Mr. Trump. “What appears to be a developing Tammany situation is really the coalescence of many consultants who pretend they have an inside track toward the endorsement. No inside track exists.”

Yet while Tammany Hall, a New York City political machine that endured for nearly two centuries, owed its longevity to its spreading around of patronage, Mr. Trump can be downright stingy. Though he holds rallies for some candidates, for many his support goes no farther than an email and a $5,000 check. Mr. Trump has almost never deployed his huge list of supporters to help other politicians raise money (Representative Elise Stefanik of New York being a rare exception earlier this year). Facing the possibility of high-profile defeats, the Trump team is now planning to spend directly to assist some vulnerable Trump-backed candidates; a cash transfer to a Georgia super PAC was only the first step.

Taylor Budowich, a spokesman for Mr. Trump, said focusing only on direct spending does not fully account for the value of the Trump imprimatur for voters and the “free media coverage” it generates. “It was once said an endorsement isn’t worth the paper it’s printed on, but there’s now a caveat to that — the Trump endorsement,” Mr. Budowich said.

Not unlike past political bosses, Mr. Trump has focused heavily on the mechanics of elections — who counts the votes, who certifies them — while ceaselessly sowing distrust in the system through false claims of vote rigging.

As Tammany’s corrupt Boss Tweed was portrayed saying, as he leaned on a ballot box in a famous 1870s cartoon: “As long as I count the votes, what are you going to do about it?”

Or, as Mr. Trump told Breitbart News this month, “There’s an expression that the vote counters are more important than the candidate, and you could use that expression here.”

Wielding power over the party and selling the fiction of a stolen election also serve to distract from Mr. Trump’s unhappy exit from the White House as a loser.

Michael D’Antonio, a Trump biographer, drew a parallel between this period and an earlier crisis in Mr. Trump’s career: his bankruptcy in the early 1990s. “These would have been ruinous events for someone else,” he said. “But for Trump it just marked a turn in his method and his pursuit of power. And he never accepted these were really losses.”

Democrats are bracing for losses in 2022. But strategists in both parties say Mr. Trump’s big public profile presents a risk for Republicans, as private surveys and focus groups show he remains a potent turnoff for swing voters.

It is a very different story in Republican primaries, where few serious candidates are openly breaking with Mr. Trump. “The takeover of the Republican Party by President Trump has been so complete,” said Boris Epshteyn, another former Trump adviser sometimes seen at Mar-a-Lago, “that even the RINOs are attempting to talk MAGA.”

‘Like crabs in a bucket’

Nothing reveals Mr. Trump’s hold on the party quite like the genuflections and contortions of those seeking his political approval.

Some candidates pay to attend Mar-a-Lago fund-raisers for others — clamoring for a fleeting moment of Mr. Trump’s attention, or better yet, a photo. “Epic moment,” was how one House contender memorialized her few seconds with Mr. Trump on Instagram.

When Mr. Trump invited candidates from Michigan to stand beside him at one event, a man’s voice rang out: “I’m running for governor too, can I come up there?” It was Ryan Kelley. “You’re running for governor of what?” a confused Mr. Trump asked. “Michigan!” Mr. Kelley replied. Up he came, shaking hands with an opponent, Perry Johnson.

Mr. Johnson, for his part, had been a repeated presence at Mar-a-Lago, proudly posting a grainy video of Mr. Trump hailing his “good poll numbers” at another fund-raiser. He had even bought a television ad welcoming Mr. Trump to Michigan before an April 2 rally.

Yet Mr. Trump snubbed him at the rally and instead praised a rival candidate, Tudor Dixon, who had held her own Mar-a-Lago fund-raiser in February.

In many ways, the endorsement chase is a real-life reprisal of Mr. Trump’s old reality-television role.

“What was ‘The Apprentice’ but a sad scramble of people behaving like crabs in a bucket to be lifted out by him?” said Mr. D’Antonio, the biographer. “How are these people anything other than contestants vying for his approval?”

In one oft-recounted scene, Mr. Trump pulled several Ohio Senate candidates into a room last year at Mar-a-Lago, where they began verbally attacking one another as he watched. “Things went off the rails,” said one candidate, Bernie Moreno, who blamed his rivals, not Mr. Trump, for the mayhem. Mr. Moreno has since dropped out, not wanting to divide the pro-Trump vote.

Nearly all the Ohio contenders have run ads touting their ties to Mr. Trump and lobbied him personally. Jane Timken calls herself “the real Trump conservative.” Josh Mandel calls himself “pro-God, pro-gun, pro-Trump.” Mike Gibbons calls himself and Mr. Trump two “businessmen with a backbone.”

Mr. Trump did not endorse any of them, instead backing the author J.D. Vance. At a debate before the endorsement, Matt Dolan, the only leading Republican contender not aggressively vying for a Trump endorsement, suggested his rivals were putting Ohio voters second. “There are people up on this stage who are literally fighting for one vote,” he said, “and that person doesn’t vote in Ohio.”

Mr. Dolan is an exception. As a rule, an audience with Mr. Trump can make or break a candidacy. So candidates strategize heavily.

Mr. Trump enjoys flattery and is not above rewarding sycophants. But insiders say bringing compelling visual material matters, too. Big fonts are key. With photos and graphics. In color.

“He’s not a real big digital guy, so we had printouts,” said Joe Kent, who has since won Mr. Trump’s backing for his effort to unseat Representative Jaime Herrera Beutler of Washington, one of the 10 Republican impeachment votes.

“I need to see polling, I need to see funding, I need to see you make a name for yourself,” Mr. Trump instructed him, as Mr. Kent recalled.

When he likes what he sees, Mr. Trump will mail words of encouragement, scrawled on news clippings with a Sharpie. “You are doing great!” he wrote in January to Mr. Kent. “You are doing great!” he wrote last October to Harriet Hageman, who is challenging Representative Liz Cheney of Wyoming.

When Representative Billy Long, a candidate for Senate in Missouri, first met with Mr. Trump last year, he brought along a favorable poll printout. But he sensed he’d been beaten to the punch when, he recalled, Mr. Trump “reached over and picked up another poll” that Mr. Long presumed came from a rival, though it could have been part of the packet Mr. Trump’s team prepares for candidate meetings.

“Donald J. Trump is going to do what he wants to do when he wants to do it,” Mr. Long said. “There is no secret sauce here.”

Precision television

Television is a popular way to lobby Mr. Trump, and some candidates try by running ads far away from their voters. When Mr. Trump was staying at his Bedminster, N.J., golf course last summer, Jim Lamon, a Senate candidate in Arizona, paid for an ad on Fox News in New Jersey.

Michele Fiore, a Las Vegas city councilwoman, announced her bid for Nevada governor with a theatrically pro-Trump commercial that ran in West Palm Beach. She later switched to the state treasurer’s race, saying in another ad that the Trump team had counseled her to lower her sights.

And in March, a group urging Mr. Trump to rescind his endorsement of Matthew DePerno, a Republican running for attorney general in Michigan, bought an ad attacking Mr. DePerno that ran in West Palm Beach.

Others have used video with even greater precision.

In November, Blake Masters, a Senate candidate in Arizona, put out a public video saying, “I think Trump won in 2020,” the day before he flew to Florida for a Mar-a-Lago fund-raiser, which records show cost his campaign $29,798.70.

Some catch Mr. Trump’s eye on television in between the commercials.

Lt. Gov. Janice McGeachin of Idaho appeared on Tucker Carlson’s Fox News program last June and sang Mr. Trump’s praises. The next day, he called her.

“It was the coolest thing,” she said, adding she “slipped it in” that she planned to challenge Gov. Brad Little, the incumbent Republican, and asked for Mr. Trump’s support. Soon, she was on a plane to New York for a meeting in Trump Tower. “The thing that I wanted to do is give him a big hug and tell him how much we loved him,” she said. “And that’s the first thing we did.”

Ms. McGeachin said she told Mr. Trump that Mr. Little hadn’t fought hard enough to overturn the 2020 election. In the fall, she pressed her case at Mar-a-Lago, and left with a signed red hat that she wears out on the stump. Soon, Mr. Trump formally endorsed her — though he had only praise for Mr. Little, who had attended a Mar-a-Lago fund-raiser for a Trump-aligned nonprofit just days before.

Ms. McGeachin, who caused a stir recently by taping a speech for a white nationalist gathering, is widely seen as an underdog in the May primary.

The episode encapsulates the peculiarities of Mr. Trump’s style as a party boss: receptiveness to intensive wooing, haphazard decision-making, the potential for him to overplay his hand and the requirement that his false claims of election fraud be amplified.

“It is the most coveted endorsement, I believe, in political history,” Ms. McGeachin said.

A heavy hand

With an eye to his win-loss record on endorsements, Mr. Trump is increasingly treating Republican candidates like game pieces to be moved, swapped or abandoned. Results have been mixed.

In Georgia, he recruited former Senator David Perdue to challenge Gov. Brian Kemp, a Republican who defied Mr. Trump by certifying the 2020 election and standing behind the result. Mr. Trump pressed the other pro-Trump candidate in the race, Vernon Jones, a former Democrat, to run for House instead, with his backing.

That maneuver worked, but polls have shown Mr. Perdue trailing Mr. Kemp heading into the May 24 contest, an early barometer of Mr. Trump’s influence.

In North Carolina, Mr. Trump tried to get an ally, Representative Mark Walker, to abandon his Senate campaign and clear the field for Mr. Trump’s choice, Representative Ted Budd, to take on former Gov. Pat McCrory in May’s primary. But after courts threw the state’s political maps into turmoil, Mr. Walker refused, threatening to split the pro-Trump vote, though polls show Mr. Budd leading anyway.

Mr. Trump has already rescinded one endorsement, Representative Mo Brooks for Senate in Alabama, after Mr. Brooks had slumped in the polls, and he could backtrack on others who are trailing. He has spoken in private, for instance, about softening his stance behind Ms. McGeachin.

Mr. Trump has been especially hands-on in recruiting challengers to his loudest Republican critics, such as Ms. Cheney.

Last year, he interviewed several potential challengers, hoping to set up a two-person showdown. Among them was Darin Smith, a Cheyenne lawyer, who flew to Bedminster and later said he regretted not putting Trump insiders on his payroll sooner. Mr. Trump eventually endorsed Harriet Hageman, a former party official, whose advisers include the current and former Trump strategists Justin Clark, Nick Trainer, Bill Stepien and Tim Murtaugh.

“Whether you love the swamp or you hate it, it’s a reality,” said Mr. Smith, who has since endorsed Ms. Hageman. “There are orbits around Trump.”

Perhaps nowhere has Mr. Trump delved more deeply into local politics than in Michigan, guided in part by the party’s co-chair, Meshawn Maddock, a close ally who arranged for buses to carry protesters to Washington on Jan. 6, 2021. In November 2020, after Mr. Trump summoned Michigan lawmakers to the White House for an extraordinary meeting as he sought to overturn the election, the state’s two G.O.P. legislative leaders rebuffed him. Now, Mr. Trump has endorsed more than a half-dozen Michigan legislative candidates to elevate Ms. Maddock’s husband, State Representative Matt Maddock, as the next state House speaker.

Mr. Trump made no bones about his desire to take control of the state’s vote-counting posts as he rallied support for his choices for state attorney general and secretary of state, Mr. DePerno and Kristina Karamo.

“Remember, this is not just about 2022, this is about making sure Michigan is not rigged and stolen again in 2024,” Mr. Trump said outside Detroit on April 2, adding, “I don’t do this often for state people — this is so important.”

Asserting dominance

Mr. Trump’s war chest certainly projects power, but it is his enduring popularity with the party’s base that most frightens other Republican leaders.

The endless stream of party fund-raising messages that use Mr. Trump’s name — and sometimes make it seem like the money goes to him — is evidence of his pull with small donors. Polls also show that most Republican voters value his endorsement. “His domination of the party at the grass-roots voter level is unprecedented,” said Mr. Stone, the longtime Trump adviser.

Fully aware of this, Mr. Trump has asserted dominance over Republican congressional leaders, too.

In the House, Mr. McCarthy, who hopes to become speaker after the midterms, has tried to keep Mr. Trump on the sidelines in some primaries, lobbying, for instance, to stop him from endorsing Representative Mary Miller of Illinois, who was drawn into the same district as Representative Rodney Davis. Mr. Trump endorsed her anyway.

“McCarthy’s legitimate fear is that the majority will be won, but that 10 House members will hang together and say, ‘We’re not voting for you or anything you want,’” Mr. Stone said. He said Mr. Trump would need to wrangle those votes.

In the Senate, Mitch McConnell of Kentucky, the minority leader, has not spoken to Mr. Trump since he left the White House, but he, too, acquiesced to Mr. Trump in backing Herschel Walker for Senate in Georgia despite some early misgivings from his team.

Those unhappy with Mr. Trump’s reign as party boss are searching for signs his grip is slipping, and several potential 2024 rivals — Mike Pence, Ron DeSantis, Chris Christie, Tom Cotton — have seemed less afraid of late to disagree publicly with Mr. Trump as they probe for possible openings.

The races in which Mr. Trump has endorsed a candidate will be studied for any dimming of his power. But the fact remains that many of those he is opposing in primaries are still running as Trump Republicans. Few see an expiration date on his dominance until and unless he declines to run again in 2024 or is defeated.

A recent appearance on the Republican National Committee’s podcast captured both the draws and drawbacks of the party’s unyielding attachment to Mr. Trump. It was, by far, the podcast’s most-watched episode on YouTube — until the site removed it for spreading misinformation.

“The power of your support cannot be underestimated,” Ronna McDaniel, the party chairwoman, had told Mr. Trump, adding, “We need you.”