He arrived in golf attire, fresh off 18 holes with his brother-in-law and Bill Shine, the recently deposed co-president of Fox News. Radio and TV have made Hannity fantastically wealthy — Forbes puts his total annual income at roughly $36 million — but as one of his oldest friends, John Gomez, told me, little has changed about Hannity’s personality in the 48 years the two men have known each other. “He’s the same guy who used to drink beers with me behind the movie theater,” Gomez said — still puckish and voluble, still possessed by an energy he seems to have trouble controlling. When he is not at his cathedralic mansion on Long Island, Hannity is frequently at a condo he owns in Florida, where he brings friends like Geraldo Rivera. Sometimes, Rivera told me, “we just sit around and listen to Bo Dietl” — a former Fox News regular and retired homicide detective who recently ran for mayor of New York — “tell war stories from back in the day.”

“I realized early on that there’s no other Sean Hannity than the one you see on television,” Rivera told me. “He’s a fire-breather who breathes fire all day and then sits down and has a drink.” Rivera recalled the release of the “Access Hollywood” tape last year, in which Trump bragged of grabbing women by their genitals. At the time, many political commentators on the right were treating the video as fatal to Trump’s presidential bid; a handful of party figures called on Trump to step aside and put his running mate, Mike Pence, on the top of the ticket. Hannity went in the opposite direction, allowing that what he called the “locker room” comments were wrong, but framing the tape as a politically motivated distraction. “King David had 500 concubines, for crying out loud!” he joked to one panelist. Later, he suggested on Twitter that it was Bill Clinton who should be investigated for sexual misconduct.

It was a pivotal moment for Hannity and for Trump, and it sealed the bond between the two men. “If you look back at those traumas,” Rivera told me, “you’ll see that Hannity steadied the whole of conservative politics during those crucial times. And I think he plays much the same role now. He’s firm in his support of the president, and woe unto you if you don’t see things the same way. He’s a shield.”

Hannity and Trump remain extraordinarily close and speak to each other regularly. President George W. Bush once called Hannity, too, “but Hannity’s and Trump’s personalities are much more in line,” a friend of Hannity’s told me, “and they’ve both come from the media world.” In their conversations, the friend continued, Hannity served as sounding board: “Hannity’s a numbers guy, Trump’s a numbers guy. He thinks there’s nothing worse than bad numbers, and he knows Hannity’s got his finger on the pulse.”

Historically, a chumminess between a president and a journalist isn’t exactly unusual — in the early 1960s, the syndicated columnist Joe Alsop often defended his friend President Kennedy with a vehemence that struck many colleagues as unseemly. What makes the Hannity-Trump alliance so unusual, says Nicole Hemmer, a scholar of media history at the University of Virginia’s Miller Center, is the extent of Hannity’s reach: “He’s talking for four hours a day. He’s got social media. He’s empowered by his new status at Fox, this massive institution of Republican power.”

To trace the arc of Hannity’s career is to appreciate how deftly he has leveraged two concurrent trends — the rightward tack of the Republican Party and the expanding influence of conservative media — to become power broker, spokesman and arbiter of the Republican base. “If I’m trying to figure out how to communicate to the American people,” Hannity’s longtime confidant Newt Gingrich told me, “there are very few people who have a better understanding of the broad base, a better intuitive understanding of the kind of folks who elected Trump. He at least matches or surpasses Rush [Limbaugh] in that understanding.”

In recent weeks, Hannity has launched ferocious assaults on Republicans he sees as insufficiently supportive of the president’s agenda, from Senator Jeff Flake of Arizona to the Senate majority leader, Mitch McConnell, whom Hannity, echoing Trump, has called “weak.” Some of the blows have clearly landed. After the Republican senator Ben Sasse, a frequent Trump critic, suggested Trump’s disparagement of press freedom ran afoul of the First Amendment, Hannity said he regretted supporting Sasse. Sasse fired back vehemently on Twitter: “Sorry, Sean — you changed, not me. Some of us still believe in the Constitution.” In October, the former speaker of the House John Boehner told a reporter for Politico Magazine that he had a conversation with Hannity in 2015 in which he told Hannity that he was “nuts.” Hannity tweeted back at Boehner: “I’m sorry you are bitter and u failed!”