Night after night on Fox, Tucker Carlson weaponizes his viewers’ fears and grievances to create what may be the most racist show in the history of cable news. It is also, by some measures, the most successful.

With singular influence — reaching far beyond Fox and the viewers who tune in to his show — Mr. Carlson has filled the vacuum left by Donald J. Trump, championing the former president’s most ardent followers and some of their most extreme views. As fervently as he has raced to the defense of the Jan. 6 rioters, so has he sown doubt and suspicion around immigrants, Black Lives Matter protesters or Covid-19 vaccines.

A New York Times examination of Mr. Carlson’s career, including interviews with dozens of friends and former colleagues, and an analysis of more than 1,100 episodes of his Fox program, shows how he has grown increasingly sympathetic to the nativist currents coursing through U.S. politics, and how intertwined his rise has been with the transformations of his network and of American conservatism.

Here are some key takeaways from “American Nationalist,” The Times’s three-part series on Mr. Carlson.

Years of talking points from the far-right fringe

Last spring, Mr. Carlson caused an uproar when he promoted on air the notion of the “great replacement” — a racist conspiracy theory, once relegated to the far-right fringe, that Western elites are importing “obedient” immigrant voters to disempower the native-born. The Anti-Defamation League called for his firing, noting that such thinking had helped fuel a string of terrorist attacks.

But this was hardly something new for Mr. Carlson. In more than 400 episodes, the Times analysis found, he has amplified the idea that a cabal of elites want to force demographic change through immigration.

Mr. Carlson’s producers often trawl the web for supporting material. In the show’s early years, clips would sometimes be sent to the network’s fact checkers, who would occasionally discover that a story had actually originated farther afield, on a racist or neo-Nazi site like Stormfront.

In a statement, Justin Wells, a senior executive producer overseeing Mr. Carlson’s show, defended the host’s rhetoric and choice of topics: “Tucker Carlson programming embraces diversity of thought and presents various points of view in an industry where contrarian thought and the search for truth are often ignored.”

He put Trumpism over Trump

In the White House, Mr. Trump had a symbiotic relationship with Fox: watching, tweeting, talking frequently to the network’s hosts. But that presented Mr. Carlson with a programming problem as his new show ascended to Fox’s marquee 8 p.m. time slot: He wanted to reach the Trump base, he told friends and co-workers, but without being beholden to the mercurial president. The solution: embrace Trumpism, not Mr. Trump.

The show would grasp the emotional core of Mr. Trump’s allure — white panic over the country’s changing ethnic composition — while keeping a carefully measured distance from the president. Mr. Carlson sometimes even criticized the president, and in private, he mocked Mr. Trump’s habit of phoning to head off on-air attacks.

He sought out stories, one friend observed, that were sometimes “really weird” and often inaccurate but tapped into viewers’ fears of a trampled-on American culture. He inveighed against Macy’s, for instance, for introducing a line of hijabs, likening it to promoting genital mutilation.

As Tucker goes, so goes Fox

Mr. Carlson forged a relationship with Lachlan Murdoch, heir apparent of the Fox empire, and cultivated a perception within the network that the two men were close. As his show became the highest-rated cable news program in prime time, Fox looked to its success as a model for a broader transformation.

Inside the network, journalists and commentators clashed over what many saw as a creeping invasion of the news division by allies of the higher-rated, pro-Trump prime-time hosts.

While Mr. Murdoch and Fox executives have often couched their defense of “Tucker Carlson Tonight” as a protection of free inquiry and controversial opinions, Mr. Carlson’s on-air provocations have long been something else: part of a painstaking, data-driven experiment that has succeeded wildly in bolstering Fox’s profit machine against the long-term decline in cable news subscriptions.

According to three former Fox employees, Mr. Carlson was among the network’s most avid consumers of what are known as minute-by-minutes — ratings data on an audience’s real-time ebb and flow. “He is going to double down on the white nationalism because the minute-by-minutes show that the audience eats it up,” said a former employee who worked frequently with Mr. Carlson.

Network executives soon began applying the approach to the daytime news shows. They pitched it as “Moneyball” for television: an audience-first approach to deciding what to cover and how to cover it.

Journalists on Fox’s daytime shows discerned a pattern to what the audience didn’t like: segments featuring Fox’s own reporters, stories deemed unfavorable to Mr. Trump, left-leaning or independent guests. Immigration, on the other hand, was a hit.

Network executives ordered up so much coverage of illegal immigrants or nonwhite Americans caught in acts of crime or violence that some employees referred to it by a grim nickname: “brown menace.”

Dismay and dissent within the network

A string of segments in 2018 about the gruesome murders of farmers in South Africa, which Mr. Carlson suggested were part of a campaign by that country’s Black-led government to seize white-owned land, sparked a rare high-level dispute inside Fox.

Brian Jones, then the president of Fox Business Network and the highest-ranking Black man in Fox leadership, explained to senior executives that Mr. Carlson’s coverage had been ripped from far-right sites, and that almost everything Mr. Carlson was saying on air was wrong. But Mr. Jones was overruled, and the coverage continued. Mr. Trump tweeted that his administration would “closely study” the seizure of white-owned land and the “large-scale killing of farmers.” Alt-right and neo-Nazi figures cheered the propaganda coup.

Later that year, Fox journalists discovered another reason for concern. An organizational chart loaded into the company’s new employee portal showed a controversial figure named Peter Brimelow — founder of the nativist website VDare — reporting directly to Rupert Murdoch. Employees who asked about his apparent role at Fox were told that Mr. Brimelow was helping with Mr. Murdoch’s memoirs — a project that most people thought their boss had abandoned in the 1990s — or writing speeches, or attached to some other Murdoch initiative. The chart soon disappeared. A Fox spokeswoman said Mr. Brimelow did not currently have any relationship with the company.

Going after his critics

Mr. Carlson’s popularity among viewers has allowed him to fend off critics outside Fox and shut down those within, from news anchors to junior employees who have objected to his rhetoric.

After an on-air feud with Mr. Carlson in 2019 over the impeachment inquiry and Mr. Trump’s efforts to pressure Ukrainian officials, Shepard Smith was reportedly warned against criticizing his fellow host. He departed Fox that October.

After a Fox producer, Dan Gallo, expressed concerns to human resources executives about recordings of Mr. Carlson defending statutory rape and calling Iraqis “semiliterate primitive monkeys,” and on-air comments by Jeanine Pirro questioning a Muslim congresswoman’s loyalty to the Constitution, Mr. Carlson learned about his complaints and confronted him face to face in Los Angeles, demanding that Mr. Gallo “do the honorable thing” and call him if he had a disagreement. Mr. Gallo offered to talk then and there, but Mr. Carlson wasn’t interested. “I’m busy,” the host said, and walked off.

Days after a mass shooting in El Paso by a white man protesting what he called the “Hispanic invasion of Texas,” Mr. Carlson declared that white supremacy was largely a “hoax.” A young Fox reporter, Cristina Corbin, tweeted, without mentioning Mr. Carlson: “White supremacy is real, as evidenced by fact. Claims that it is a ‘hoax’ do not represent my views.” The host called Ms. Corbin and yelled at her to “shut your mouth,” according to a former Fox executive briefed on the episode. When asked about the incident by Fox management, Mr. Carlson denied making the call.

His playbook sent sponsors fleeing, yet nearly doubled ad dollars

Here is the “Tucker Carlson Tonight” playbook: Go straight for the third rail, be it race, immigration or another hot-button issue; harvest the inevitable backlash; return the next evening to skewer critics for how they responded. Then, do it all again. This feedback loop drove up ratings and boosted loyalty to Fox and Mr. Carlson.

What it did not do was endear Mr. Carlson to advertisers. As blue-chip sponsors fled, Fox filled the space with in-house promos — using Mr. Carlson’s popularity to push other Fox shows — and direct-to-consumer brands like MyPillow, whose chief executive is a major promoter of Mr. Trump’s stolen-election lie.

Last May, after promoting the white supremacist “replacement” theory, Mr. Carlson had half as many advertisers as in December 2018. But he brought in almost twice as much money.