“I’m a Leninist,” Steve Bannon told a writer for The Daily Beast, in late 2013. “Lenin wanted to destroy the state, and that’s my goal, too. I want to bring everything crashing down, and destroy all of today’s establishment.”*

At the time, Bannon was the executive chairman of Breitbart News, the far-right news site. When he became the C.E.O. of Donald Trump’s campaign, in August, he told the writer that he had no recollection of the conversation. On Sunday, Trump, in his first personnel decisions as President-elect, named Bannon as his chief strategist and senior counselor and Reince Priebus, the Republican National Committee Chairman, his chief of staff.

The press release from the Trump transition staff said that Bannon and Priebus would be “equal partners.” This is a signal to Washington that Bannon will be the most powerful person in Trump’s White House. On November 6, 2008, the day after his election, Barack Obama made just one personnel announcement: that Congressman Rahm Emanuel would be his chief of staff. Every staff member in the Obama White House reported to Emanuel, including political advisers such as David Axelrod. Even in the George W. Bush White House, which at first had a weak chief of staff, Andy Card, and a powerful political adviser, Karl Rove, everyone, including Rove, formally reported to Card.

Trump has indicated that, in his White House, Bannon will be first among equals.

Before the announcement, there was speculation that Bannon and Priebus were competing for the job of chief of staff, which, as Axelrod noted yesterday, “has inherent authorities that advisers do not.” But with those authorities come responsibilities that can limit the person in the role. Walter Mondale, the second Vice-President to have an office in the West Wing, advised his successors to avoid taking on managerial responsibilities (such as Al Gore’s National Partnership for Reinventing Government). The key to influence in any White House is simply to establish oneself as the President’s most important adviser. This seems to be the role that Bannon has created for himself.

Bannon, who is sixty-two, has spent his relatively short political career incubating the nationalist right that roared to life in the wake of the 2008 financial crisis and gathered strength through the Obama years. He grew up in Virginia, served in the Navy, went to Harvard Business School, and spent years as a mergers-and-acquisitions dealmaker for Goldman Sachs. In 2008, he became fascinated by Sarah Palin, the Republican Vice-Presidential candidate, and the crowds she attracted. He spent the next eight years making hagiographic films about Palin and other right-wing political figures, and transforming Breitbart, which he took over after the death of its founder, Andrew Breitbart, in 2012, into a center for the insurgent populist movement.

As Kurt Bardella, the former spokesman for Breitbart, told me earlier this year, when I was researching a piece on Bannon, “When Sarah Palin was on the rise, he had found a way to become a part of that circle. When the Tea Party was on the rise, he seemed to be right there in that circle. When it was going to be Ted Cruz, he was there. When it was going to be Ben Carson for a hot second, he was there. He’s been someone who’s been in pursuit of that pipeline to power for a long time now.”

The turning point for Bannon, Breitbart, and the movement that would eventually coalesce around Trump was the 2013 debate over immigration reform. After Mitt Romney lost to Barack Obama, in 2012, the Republican leadership, encouraged by the business wing of the G.O.P. and the Party’s consultant class, made comprehensive immigration reform a legislative priority. Fox News became sympathetic to the effort and Priebus, then the chairman of the R.N.C., issued a report declaring that passing immigration reform was necessary for the survival of the Party.

This was the opening that Bannon had been looking for. He despised Fox News and Rupert Murdoch, whom he believes is a “globalist,” and he saw Priebus and the Republican leaders in Congress, such as Paul Ryan and Eric Cantor, as “enemies.” Breitbart became the hub of resistance to the immigration-reform effort, developing strong ties to Alabama Senator Jeff Sessions, who was leading the opposition in the Senate. More ominously, it started cultivating a little-noticed movement of disenchanted conservatives who argued that the right should promote a restoration of white culture.

Under Bannon, Breitbart, which was read by Republicans across the political spectrum, allowed this so-called alt-right movement to enter the mainstream conservative conversation. The site published a tag on “black crime.” Bannon sent reporters to the Mexican border to cover immigration from the perspective of American citizens who felt victimized by undocumented immigrants. Breitbart writers used traditional tropes of anti-Semitism, attacking international bankers and globalists. “We’re the platform for the alt-right,” Bannon told Sarah Posner, of Mother Jones, in July, weeks before he became the chairman of Trump’s campaign.

Breitbart boosted any political outsider who threatened Republican leaders. In 2013, it cheered Ted Cruz when he helped shut down the government. In 2014, it promoted David Brat, who defeated House Majority Leader Eric Cantor in a primary by attacking his Wall Street ties and alleged sympathy for amnesty. It helped instigate the rebellion against Speaker John Boehner, who resigned from Congress in 2015. Bannon tried to entice Sessions into a race for the White House, but he declined.

During the Republican primaries, Breitbart savaged Jeb Bush and Marco Rubio. By the fall of 2015, the site had become a Trump propaganda machine: “Trumpbart News” to its critics. In March, when Corey Lewandowski, Trump’s campaign manager, grabbed Michelle Fields, a Breitbart reporter at the time, when she tried to ask Trump a question, Bannon sided with the Trump campaign, which denied that the incident even occurred. Bannon formally joined the Trump campaign as C.E.O. in August, when Paul Manafort, the former chairman, became mired in a scandal involving financial ties to a pro-Russian party in Ukraine.

During the campaign, Bannon kept an article from Politico over his desk that included some gloating by Clinton staffers about the landslide win that they expected. He believed that Clinton was weaker with Hispanics, African-Americans, and white millennials than Obama was in 2012. And he believed that, with a surge of white working-class support, Trump could win Wisconsin and Michigan, which had voted Democratic since the nineteen-eighties. He was right about all of this.

Bannon injected Trump’s speeches with language about global élites and bankers. Clinton “meets in secret with international banks to plot the destruction of U.S. sovereignty,” Trump said in an October speech that was so disturbing in its coded anti-Semitism that the Anti-Defamation League spoke out against it. Trump’s final TV ad of the campaign combined excerpts from the speech, decrying “those who control the levers of power in Washington,” with images of George Soros, Janet Yellen, and Lloyd Blankfein, all of whom are Jewish. “This needs to stop,” Jonathan Greenblatt, the head of the A.D.L., said in a statement.

When Bannon has been asked about these racist and anti-Semitic appeals, he has insisted, implausibly, that he favors nationalism, not white nationalism. “If you look at the identity movements over there in Europe, I think a lot of [them] are really ‘Polish identity’ or ‘German identity,’ not racial identity,” he told Posner. “It’s more identity toward a nation-state or their people as a nation.” Bannon sees those European movements as allies, and has cultivated ties with far-right parties in the U.K., France, Germany, the Netherlands, and Italy. The first foreign political leader who President-elect Trump met with was Nigel Farage, a friend of Bannon who attended the Republican National Convention and campaigned with Trump in Mississippi, in July. Marine Le Pen, the leader of France’s far-right National Front, who is running for President, has already cited Trump’s victory as a harbinger of her own. Her niece, Marion Maréchal-Le Pen, a member of the French parliament, tweeted, “I answer yes to the invitation of Stephen Bannon, CEO of @realDonaldTrump presidential campaign, to work together.”