Last week, when Donald Trump tapped the chairman of Breitbart Media to lead his campaign, he wasn't simply turning to a trusted ally and veteran propagandist. By bringing on Stephen Bannon, Trump was signaling a wholehearted embrace of the "alt-right," a once-motley assemblage of anti-immigrant, anti-Muslim, ethno-nationalistic provocateurs who have coalesced behind Trump and curried the GOP nominee's favor on social media. In short, Trump has embraced the core readership of Breitbart News.

"We're the platform for the alt-right," Bannon told me proudly when I interviewed him at the Republican National Convention (RNC) in July. Though disavowed by every other major conservative news outlet, the alt-right has been Bannon's target audience ever since he took over Breitbart News from its late founder, Andrew Breitbart, four years ago. Under Bannon's leadership, the site has plunged into the fever swamps of conservatism, cheering white nationalist groups as an "eclectic mix of renegades," accusing President Barack Obama of importing "more hating Muslims," and waging an incessant war against the purveyors of "political correctness."

"Andrew Breitbart despised racism. Truly despised it," former Breitbart editor-at-large Ben Shapiro wrote last week in Daily Wire, a conservative website. "With Bannon embracing Trump, all that changed. Now Breitbart has become the alt-right go-to website, with [technology editor Milo] Yiannopoulos pushing white ethno-nationalism  as a legitimate response to political correctness, and the comment section turning into a cesspool for white supremacist mememakers."

Exactly who and what defines the alt-right is hotly debated in conservative circles, but its most visible proponents—who tend to be young, white, and male—are united in a belief that traditional movement conservatism has failed. They often criticize immigration policies and a "globalist" agenda as examples of how the deck is stacked in favor of outsiders and elites instead of "real Americans." They bash social conservatives as ineffective sellouts to the GOP establishment, and rail against neo-conservative hawks for their embrace of Israel. They see themselves as a threat to the establishment, far bolder and edgier than Fox News. While often tapping into legitimate economic grievances, their social media hashtags (such as #altright on Twitter) dredge up torrents of racist, sexist, and xenophobic memes.

Trump's new campaign chief denies that the alt-right is inherently racist. He describes its ideology as "nationalist," though not necessarily white nationalist. Likening its approach to that of European nationalist parties such as France's National Front, he says: "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. It's more identity toward a nation-state or their people as a nation." (Never mind that National Front founder Jean Marie Le Pen has been fined in France for "inciting racial hatred.")

Bannon dismisses the alt-right's appeal to racists as happenstance. "Look, are there some people that are white nationalists that are attracted to some of the philosophies of the alt-right? Maybe," he says. "Are there some people that are anti-Semitic that are attracted? Maybe. Right? Maybe some people are attracted to the alt-right that are homophobes, right? But that's just like, there are certain elements of the progressive left and the hard left that attract certain elements."

A Twitter analysis conducted by The Investigative Fund using Little Bird software found that these "elements" are more deeply connected to Breitbart News than more traditional conservative outlets. While only 5 percent of key influencers using the supremacist hashtag #whitegenocide follow the National Review, and 10 percent follow The Daily Caller, 31 percent follow Breitbart. The disparities are even starker for the anti-Muslim hashtag #counterjihad: National Review, 26 percent; Daily Caller, 37 percent; Breitbart News, 62 percent.

Bannon's views often echo those of his devoted followers. He describes Islam as "a political ideology" and Sharia law as "like Nazism, fascism, and communism." On his Sirius XM radio show, he heaped praise on Pamela Geller, whose American Freedom Defense Initiative has been labeled an anti-Muslim hate group by the Southern Poverty Law Center. Bannon called her "one of the leading experts in the country, if not the world," on Islam. And he basically endorsed House Speaker Paul Ryan's primary challenger, businessman Paul Nehlen, who floated the idea of deporting all Muslims from the United States.

During our interview, Bannon took credit for fomenting "this populist nationalist movement" long before Trump came on the scene. He credited Sen. Jeff Sessions (R-AL)—a Trump endorser and confidant who has suggested that civil rights advocacy groups were "un-American" and "Communist-inspired"—with laying the movement's groundwork. Bannon also pointed to his own films, which include a Sarah Palin biopic and an "exposé" of the Occupy movement, as "very nationalistic films." Trump, he said, "is very late to this party."