Devil’s Bargain, Joshua Green’s highly readable account of the relationship between Steve Bannon and Donald Trump, should carry a health warning. There is something about the cast of characters — a collection of far-right activists, oddball billionaires, and political opportunists — littering its pages that can leave readers feeling queasy.

The principal supporting actor in this grim production is Bannon, Trump’s former chief strategist. A conservative Catholic from a working-class, Irish-American home, his “kaleidoscope career” — encompassing spells in the navy, Goldman Sachs and Hollywood — settled on politics just over a decade ago after a chance meeting with Andrew Breitbart.

One of that rare breed of Jewish conservative activists, Breitbart was about to launch his eponymous news website. With Breitbart’s encouragement, Bannon, who had been “dabbling in minor Hollywood moguldom”, began to churn out right-wing documentaries. Breitbart — whose journalistic ethics are such that Fox News barred him as an on-air guest — admiringly termed him “the Leni Riefenstahl of the Tea Party movement”.

With Breitbart’s sudden death in 2012, Bannon was thrust centre-stage. Taking the helm at Breitbart News, he doubled-down on its founder’s vision. With its racially charged, populist agenda, the site became the flagship of the alt-right, the “rolling tumbleweed of wounded male id and aggression”, which would later provide many of the online warriors in Trump’s campaign.

But Bannon’s ambitions — this is a man who has on his office wall an oil painting of himself dressed as Napoleon, a gift from Nigel Farage — stretched wider than Breitbart News.

He thus worked to place himself at the centre of what Hillary Clinton once dubbed the “vast, right-wing conspiracy” that sought to drive her husband from office; a conspiracy which was now determined to ensure another Clinton did not sit in the White House.

Bankrolled by eccentric billionaire Robert Mercer (who once donated to a Republican congressional candidate who believed the secret of extending human life lay in preserving thousands of urine samples), this consisted not only of a supposedly non-political research institute, but also a film production company and a cutting-edge data analytics company. It eventually proved fatal to Mrs Clinton’s hopes.

It is at this point that Green’s leading man, Donald Trump, makes his appearance. What Trump lacked in beliefs (he appears to have few, other than an enduring belief in his own greatness), Bannon more than made up for. He provided the aspiring presidential candidate with what Green aptly characterises as an internally coherent, nationalist world-view that taps into Trump’s own gut instincts. Trump dubbed it “America First” (“I don’t care,” he responded when told it echoed Charles Lindbergh’s antisemitic America First committee) and, with Bannon cheer-leading from Breitbart, began to build a political movement rooted in white identity politics.

It is a noxious cocktail, which frequently spews clouds of antisemitism. Jewish journalists, for instance, frequently found their Twitter feeds deluged with antisemitic imagery (the Anti-Defamation League later calculated that 2.6 million Tweets were sent in the year leading up to the election, with the perpetrators disproportionately likely to self-identify as Trump supporters or part of the “alt-right”).

Neither candidate nor campaign manager appeared unduly concerned (the latter often rejecting the suggestion of any association with antisemitism by noting that both Breitbart and Breitbart News’s president, Larry Solov, were Jewish). Indeed, Trump’s closing campaign ad which featured three Jews — George Soros, Federal Reserve chair Janet Yellen and Goldman Sachs chief executive Lloyd Blankfein — and warned of a “global power structure”, which “robbed” working-class Americans, earned a justified rebuke from the ADL. “Darkness is good,” Bannon told Trump in response. “Don’t let up.”

Green’s description of the manner in which Trump and Bannon combined “power and reach”, thereby ensuring they achieved “strength and influence far beyond what either could have achieved on his own” is his book’s strongest feature.

Since its publication, Bannon has left his role at the White House and Trump, in adopting much of the agenda of the Republican right, has abandoned many of his populist nationalist pledges, if not the rhetoric that accompanied them.

On the morning after Trump’s election, a reporter suggested to Bannon their story had all the makings of a Hollywood movie. “Brother,” he replied, “Hollywood doesn’t make movies where the bad guys win.”

Robert Philpot’s books include ‘The Honorary Jew’, a study of Margaret Thatcher, (Biteback Publishing)