Six months into Donald Trump’s presidency, the bond between him and his base remains strong, largely unaffected for now by the mounting scandals, talk of impeachment, and Trump’s stalled agenda. There have been five special elections to fill vacant House seats—in Georgia, Montana, Kansas, California, and South Carolina—and the Republicans have won four of them. In Georgia, the most closely watched race, the Democrats poured in $30 million for their candidate. But the Republicans nearly matched that figure, and their narrow victory in June was perceived as a win for Trump—and Trumpism, however ill-defined it may be.

Joshua Green’s new book, Devil’s Bargain, argues that Trumpism is best understood through his partnership with Stephen K. Bannon, now the president’s chief political strategist. Green, formerly a correspondent at The Atlantic and now at Bloomberg Businessweek, has been writing about conservatives since the George W. Bush years. It is a testament to his adroit intertwining of Bannon’s story with Trump’s that we’re not certain which of the two figures has sold the bigger part of himself to the other. In the broader sense, they are coauthors of our moment’s tabloid conservatism.

Trump has had many biographers, but it was Green who did the first in-depth reporting on Bannon, in a long Bloomberg profile in October 2015, ten months before Bannon formally joined the Trump campaign and rescued it from what looked like certain defeat. Previously, Bannon had been an informal adviser while making Breitbart News, the website he had run since 2012, Trump’s main propaganda auxiliary, surpassing Fox News, which had been divided over Trump and roiled by a sexual harassment scandal involving the network’s late founder and CEO, Roger Ailes. Green describes a conversation in which Ailes, still clinging to his job, tells Bannon he can survive. He just has to plead his case directly to Rupert Murdoch, who is away on his boat and can’t be reached. Bannon sees the obvious, telling Ailes, “If somebody called him about a merger, he’d take the fucking call…. You’re done.” A patois of coarseness is heard everywhere in this book, but especially from its two principals. Bannon was able to manage Trump the candidate when other, more seasoned operatives could not because Bannon is Trump’s unlikely spiritual twin, his bookish doppelgänger, unkempt in cargo shorts.

Bannon is by upbringing and temperament a son of the embattled South, a working-class Catholic who grew up in Richmond, Virginia, when the state was still a backward fief, ruled by Senator Harry F. Byrd Jr., an early leader of Southern “massive resistance” to civil rights. From the start, Bannon seems to have been a younger version of Pat Buchanan: a noisy, brawling, bred-in-the-bone anti-Communist. Educated by Benedictines at a Catholic military school, he went on to Virginia Tech and then enlisted in the Navy in 1977. He was a navigator on a destroyer in the North Arabian Sea in 1980…