“Now you got four years where we know what we’re doing, where we have a chance to start from scratch with people who we know are absolute warriors for the movement,” he said on conservative activist Charlie Kirk’s podcast last week. “Now you’re stuck with that for four years.”

It was Don Jr who saw the early threat that Robert F. Kennedy Jr’s candidacy posed to his father’s campaign, and who, allies say, tried to brainstorm ways to bring him into the fold.

Since Kennedy was chosen as the nominee for Health and Human Services secretary, Don Jr has kept him close, even feeding the notoriously health-conscious Kennedy a McDonald’s burger aboard his father’s plane and then taking a picture of it.

This is a tactic Kirk suggested was akin to a mob strategy: “If you think someone is an informant, you make them take a little drugs,” he suggested during the podcast interview.

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“Bobby did have some McDonald’s,” Don Jr said. “We definitely had some fun with that one.”

Loyalty first

This loyalty-first approach explains how and why Matt Gaetz, a fierce Trump defender, was selected as the nominee for attorney general. (The subject of an investigation involving sex trafficking, Gaetz pulled himself out of consideration on November 21.)

It explains how Sergio Gor, Don Jr’s business partner at Winning Team, their conservative publishing company, was selected to lead the White House Personnel Office. And it explains how J.D. Vance, the vice president-elect, was chosen as well.

Each choice amounted to a set-it-and-forget-it guarantee, not only for a president who demands fealty but also for a son prepared to enforce his father’s demands.

Don Jr declined a request for an interview through a spokesperson, but others who are close to him were cleared to speak on his behalf, including Kirk. “He only weighs in when something is particularly important to him,” Kirk said, “or where he feels as if there might be something that would not be in his father’s best interest.”

Topics that are most important to him include issues around the Second Amendment, the border, privacy and foreign policy, several allies said, with one prominent example: Don Jr was an early champion of Vance because the two men shared the belief that the United States should stop the flow of aid to Ukraine.

He is also a crusader in the so-called anti-woke movement, and seems to revel in being hated and feared by liberal Americans who accuse him of harmful and divisive beliefs. Week after week, he publishes a torrent of posts on social media, targeting an array of topics and people that are red meat to the MAGA base, from transgender Americans to members of the news media.

A prime example of Don Jr’s typical fare appeared on his Instagram account last week, when he asserted that “biological & objectively attractive women are allowed to win beauty pageants again. WE ARE SO BACK!!!” The post drew a fire emoji from Elon Musk, the world’s-richest-man-turned-MAGA-surrogate. On Kirk’s podcast, Don Jr said that he and Musk recently spent three hours aboard the president-elect’s plane “talking about space”.

“He has a real commitment to developing both the policies and the personnel,” said Newt Gingrich, the former House speaker, who was recently a guest on Don Jr’s podcast. “He’s a sentinel trying to defend the president and Trumpism from people who would like a job but don’t necessarily have the right credentials to do it.”

This means that other threats, such as former South Carolina governor Nikki Haley, a first-term appointee who later fell out of favour for, among other things, criticising Trump’s response to the riot at the Capitol, have not fared as well. She is now a figure of mockery for the president-elect’s son. When Haley criticised Trump’s cabinet picks this week, Don Jr, as he often does, used social media to fire back.

“If Nikki Haley really wants a Cabinet filled with neocon warmongers to satisfy the billionaire donors that control her, she should try running for President and winning herself,” he wrote.

“Oh wait, I forgot she already tried that and lost in a landslide.”

An evolving relationship

For a son who at times has taken pains to differentiate himself from his father, on style if not substance, he has remarked to associates that, as it turns out, he might be more like his father than he initially realised.

He has long embraced his father’s grievance-based brand of politics. He is ubiquitous at Trump rallies, on social media and on conservative podcasts, serving as a megaphone for Trump’s base, rather than trying to lead from inside.

“He’s on the outside. He has his businesses,” Gor said. “Sometimes people on the outside like Don have more influence than people on the inside.”

It is a striking evolution for a father-son relationship that has at times been distant and tense.

He did not speak to his father for a year after Trump divorced his mother, Ivana, during an affair with Marla Maples, who would become Trump’s second wife. While his father enjoyed the perks of life in towers and seaside mansions, Don Jr, who was taught to hunt and fish by his maternal grandfather, preferred life outdoors. (A father of five, he will leave his father’s side to go on a Thanksgiving-week hunting trip with one of his children.)

And, in 2017, he earned Trump’s ire for becoming a central figure in the investigation into the Trump campaign’s ties to Russia – earning him a reputation with the first-term White House as being reckless. His nickname among some first-term aides was Fredo – as in the hapless eldest son of the fictional Corleone family, according to one of those aides.

He is still careful not to ever try to eclipse his father, a half-dozen associates said, but he has since proved himself and his value to Trump. He has turned his efforts to identifying and cultivating a new generation of MAGA-loyal politicians, including Vance and several new Republican senators in the next Congress, such as Bernie Moreno of Ohio, Tim Sheehy of Montana and Jim Banks of Indiana.

“If you have a son who is smart, hardworking and wants to help you,” Gingrich said, “you sort of have to think, why wouldn’t you listen to him on occasion?”