In March, I went to the White House to visit Steve Bannon, who today was fired by President Trump. After Bannon showed off his office and his famous whiteboard, we sat down at a wooden conference table in the large corner office of Reince Priebus, who was then the White House chief of staff. Moments earlier, Priebus had left the building, and Bannon seemed to use the chief of staff’s office as if it were his own, roaming around while he talked, and flinging a Coke can in Priebus’s trash bin, as if he were marking territory. Despite the show of confidence, Bannon felt like he was beset by enemies.

Since the day after the election, Bannon had been fighting against forces that he believed were trying to roll back the promises of the Trump campaign. The whiteboard was so important to Bannon because it represented the policy ideas that he had been instrumental in foisting on Trump. And Bannon wanted everyone who came into the West Wing to know precisely what Trump was elected to enact: a Muslim ban, a border wall, a protectionist trade agenda (especially with China), and a more isolationist foreign policy. Bannon was obsessed with defeating the elements in the White House who hadn’t worked on the campaign and didn’t understand those policies.

“Did you see the lead story in today’s Financial Times?” Bannon asked me. He summoned an aide to retrieve it and threw the pink broadsheet, the paper of record for what he calls the global élite, on the table.

“The lead story is ‘explosion of civil war in White House, fiery debate in Oval Office,’ ” Bannon said. The story was one of many then detailing the internal combat between Gary Cohn, Trump’s top economic adviser, and Bannon. What was somewhat unusual was that Bannon was bragging about it. In previous White Houses, officials downplayed this sort of internal combat, insisting that everyone was united around the President’s agenda. But in the Trump White House there is no Trump agenda. There is a mercurial, highly emotional narcissist with no policy expertise who set up—or allowed his senior staffers to set up—competing ideological fiefdoms that fight semi-public wars to define the soul of Trumpism.

The March meeting in the Oval Office was a pivotal battle between the two main factions: what the Financial Times called the “economic nationalists close to Donald Trump” and the “pro-trade moderates from Wall Street.” Bannon had spent every hour since Election Day fighting to preserve the Trump of the campaign—raw, populist, unapologetically nativist, anti-corporate. And Bannon, at least back in March, before he ran afoul of Jared Kushner and Trump and was almost booted out of the White House, seemed to be succeeding. At Bannon’s direction, Trump hung a painting of Andrew Jackson, a hero to the nationalists, in the Oval Office. Bannon installed himself on the National Security Council as principal, putting himself on par with the Secretaries of Defense and State. The President issued a series of decrees from Bannon’s punch list: the travel ban on majority-Muslim countries, a budget with vast new funding for a border wall and ICE agents, withdrawal from the Trans-Pacific Partnership. Everything seemed to be going according to plan.

In January, 2013, Bannon, Stephen Miller, and Jeff Sessions had dinner in Washington to talk about the 2016 Presidential campaign. Barack Obama had just won reëlection, and the reigning explanation for his victory was that an unstoppable demographic surge of nonwhite voters had given Democrats a lock on the Electoral College. Most political strategists argued that the Republican Party was doomed unless it could crack the Hispanic vote, and that the only way to do that was for the G.O.P. to embrace comprehensive immigration reform that included a pathway to citizenship for millions of undocumented immigrants living in America—amnesty. The three men plotted a way to stop the coming push for immigration reform.

That same month, there was another dinner happening in New York. Rupert Murdoch and Roger Ailes met with Senators Marco Rubio and Chuck Schumer, who pleaded with the Fox News leaders to soften the network’s coverage of the immigration debate, and Fox eventually did that. The four men plotted a way to help Republicans pass immigration reform.

Bannon’s path to nationalism is famously circuitous. He grew up near Richmond, Virginia, in a big Irish Catholic family of Kennedy Democrats. Although he came of age in the late sixties, his high school, a religious military academy where he was taught by monks, kept him away from the mass protests happening in nearby Washington. He went to college at Virginia Tech, where he became the student-government president after attacking his opponent for offering only “Platitudes, Promises and Slogans.” Bannon says it was during the first years of an eight-year stint in the Navy, from 1977 to 1985, that he became reliably conservative, because of the way Jimmy Carter dealt with the Iran hostage crisis. A military-history buff, he took night classes at Georgetown and earned a master’s degree in national-security studies, in 1983, and then a degree from Harvard Business School, in 1985. In the nineties, he was deeply entrenched in New York finance, as a Goldman Sachs mergers-and-acquisitions executive, and then in Hollywood, as a somewhat marginal producer who tried, and failed, to move from the deal-making side of the business to the creative side.

In 2008, at the dawn of the Tea Party, Bannon was in Shanghai working on one of his numerous side projects, creating a virtual market inside the popular online game World of Warcraft. He persuaded Goldman to invest sixty million dollars in the effort, but it tanked, and Bannon was looking for his next reinvention. “I came back right before the 2008 election and saw this phenomenon called Sarah Palin,” he told me last year. The neo-populist movement that Trump eventually rode to victory was being born in the waning days of that campaign. Bannon thought that Republicans, who had become the party of tax cuts and free-market libertarian philosophy, exemplified by people like Paul Ryan, didn’t yet have the right vocabulary to speak to its own base. “The Republicans would not talk about anything related to reality,” he told me. “There was all this fucking Austrian school of economic theory.”

Bannon started making what are essentially crude propaganda films about people and issues on the new populist right, including ones about Palin, Ronald Reagan, Michele Bachmann, Phyllis Schlafly, and the Tea Party. He became a fixture on the conservative-conference circuit and befriended Andrew Breitbart, a former blogger and then a new-media entrepreneur who was the hidden talent behind the success of both the Drudge Report and the Huffington Post. Bannon helped Breitbart raise money for Breitbart News Network, including a ten-million-dollar investment from the Mercer family, which during this period emerged as a crucial patron for the populist right. When Breitbart died, in March, 2012, Bannon took over editorial control as well. Traffic exploded, from eleven million page views per month to two hundred million. “Frankly that’s why, when Breitbart puts its fucking gun sights on you, your life changes,” Bannon bragged to me once.

His main target became the Republican establishment. After Obama’s reëlection, when the G.O.P. started to organize itself around immigration reform, Bannon was desperate to find someone who could become the face of the populist resistance. He was hoping it would be Sessions. Meanwhile, Sessions and Miller, his top aide, were desperate to find a conservative media platform that would help them oppose immigration reform. They were all running out of time. The Republican National Committee itself, then led by Priebus, was about to release a formal report calling on the Party to adopt comprehensive immigration reform.

The Sessions-Bannon-Miller dinner in Washington in early 2013 lasted five hours. Bannon tried to convince Sessions to run for President in 2016. “You’re not going to win the Presidency, and you’re not going to win the Republican primary,” Bannon recalled telling him. “But we are going to be able to get these ideas into the mainstream. Trade is the No. 100 issue right now. We’ll make immigration the No. 1 issue, and we’ll make trade the No. 2 issue.” Sessions told Bannon and Miller that he didn’t want to run.

In the following months, during the debate over immigration, Breitbart became a crucial platform for anti-reform efforts, and Miller fed the site a steady stream of leaks from the Senate. It was also when the site started to attract white nationalists who saw restrictionist immigration policies as a weapon to keep nonwhites out of America. The site used a tag called “black crime” for some stories and brought in Milo Yiannopoulos, who wrote an infamous essay celebrating the alt-right, for which Bannon later bragged Breitbart had become “the platform.”