Donald Trump is US president because just under 80,000 people in Pennsylvania, Michigan and Wisconsin flipped those states his way. Many of his extra voters were working-class white men who had voted for Obama in 2012 and switched because of Trump’s pledge to bring jobs back to the rust belt. They may not have liked Obama’s liberal policies on gay people and guns, but – for them – the big issue remained the economy.

But Trump would not have won without the support of three other groups: his gains in suburban and rural counties outweighed Hillary Clinton’s success in the big cities; despite the reservations of the Republican establishment about his candidacy, Trump retained the party’s base, particularly among religious voters (the three times married “pussy-grabber” won more than 80% of white evangelicals); and he energised a movement of supporters that gained him the Republican nomination, without which he wouldn’t have got any votes at all.

In Alt-America, journalist David Neiwert argues that Trump won not because of economic stagnation in the northern midwest, but because a far-right racist movement had been growing since the early 90s, which both enabled Trump’s victory and has been legitimised by it. Neiwert’s narrative begins with the end of the Reagan-Bush Sr era, the election of Bill Clinton and the rise of a citizens’ militia and survivalist movement, fuelled by fears of gun control and by hostility towards Mexican immigration (against which Patriot militias mounted vigilante operations along the southern border).

Inspired by conspiracy theories about shadowy elites seeking to bring about an internationalist “new world order”, these groups partly arose out of white supremacist movements in the civil rights era (including the White Citizens’ Councils and the Ku Klux Klan). They came to public prominence through a series of dramatic stand-offs – usually over weapons issues – between armed groups and federal agents, most notably in Ruby Ridge, Montana, where a group of Militia of Montana members resisted for 10 days in 1992; and in Waco, Texas, the following year, when a 51-day siege ended in the death of cult leader David Koresh and the immolation of 76 of his followers. At the same time, “suit and tie” academic racists developed white nationalist theories in respectable guise.

During the Bush Jr years the Patriot militias declined in influence – not least because many of their members opposed George W’s initially popular war on terror, and some were conspiratorialist “truthers” who thought 9/11 was a government plot. But the movement reemerged in response to the prospect and then the fact of America’s first black president. From the day of his victory, the Obama years saw a marked increase in far-right terror attacks and a renewal of 90s-style armed stand-offs with the feds.

Meanwhile, a new far-right nexus was emerging with a range of views. The year before Obama’s 2008 victory, Andrew Breitbart founded his news website, to be taken over following his death by Steve Bannon (later to head the Trump campaign). In the same year, rightwing libertarian Ron Paul kicked off his presidential campaign with a re-enactment of the Boston Tea Party, inspiring a movement militantly opposed to Obama’s stimulus package and – even more virulently – to his affordable care proposals. Launched as a movement shortly after Obama’s 2009 inauguration, the Tea Party cause was taken up by the (relatively) mainstream Fox News, and in particular its TV jock presenter Glenn Beck, who claimed that Obama’s election was the result of the electorate’s stupidity (“I mean, we should thin out the herd, you know?”).

For Neiwert, Fox’s support for the Tea Party served as “a mechanism to mainstream the far-right”, melding Patriot conspiracists with more conventional, Fox-watching conservatives. At the same time a “lethal union” of conspiratorialists, white supremacists, Patriots and Tea Partiers gave birth to the “alt-right”, a largely online association of young, male, white nationalists. Its title coined by white nationalist (and doctoral graduate) Richard Spencer, its symbol a cartoon frog, the alt-right is self-consciously outrageous and culturally knowing. On Trump’s inauguration day, Spencer held a press conference at which he declared America “a white country, designed for ourselves and our posterity”, raised his arm in a Nazi-style salute and shouted: “Hail Trump! Hail our people! Hail victory!”

Of course, the fact that the far-right supports Trump doesn’t mean that he or his followers support it back. But Trump has been quick to associate himself with groups such as the Tea Party and slow to disavow groups to its right. In 2015, he endorsed Ann Coulter’s Adios, America – notwithstanding that in the book she described Mexican culture as “obviously deviant”. In the same year, he gave an interview to truther conspiratorialist Alex Jones, who later commented that it was “surreal to talk about issues here on air and then word for word hear Trump say it two days later”. During the 2016 campaign, Trump was criticised for initially refusing to disavow former Ku Klux Klan leader David Duke (ultimately he disavowed him). As president, he insisted this August that fascists and anti-fascists were equally to blame for clashes at a far-right rally in Charlottesville – attended by Spencer and Duke – during which one anti-fascist died.

But the most persuasive evidence for the far-right’s influence on Trumpism is ideological. Trump’s rhetoric has been more blatantly racist than just about every mainstream presidential candidate (Mexicans as “criminals, drug dealers, rapists”); his proposed ban on immigrants from some Muslim countries is clearly Islamophobic; and he embraces much of the conspiratorialist ideology that holds the far-right together. He isn’t a truther but he was a prominent “birther” (questioning Obama’s birth in Hawaii, a key conspiratorialist cause). And, crucially, he supports the idea of an international globalist conspiracy against America. So neo-Nazi (and alt-right associate) Matthew Heimbach calls for nationalists to “stand united against our common foes, the rootless international clique of globalists and bankers that wish to dominate all free people on the Earth”. Last October, Bannon co-wrote a Trump speech claiming that Hillary Clinton “meets in secret with international banks to plot the destruction of US sovereignty in order to enrich these global financial powers”.

The conspiracy theory is particularly potent because – in its various forms – it straddles the spectrum of US right thinking: from antisemites, who have always believed in a communist/capitalist Jewish conspiracy; via contemporary conspiratorialists, who claim a common interest between the international global elite, international institutions and multinational migration; to Reaganite conservatives who sought to draw a fault line between the state bureaucracy and its welfare clients on the one hand and “producers” on the other. Neiwert’s conclusion is not that Trump is a fascist, but that his campaign served as a gateway drug to those who are.

He quotes Robert Paxton’s 2005 persuasive definition of fascism as a form of political behaviour marked “by obsessive preoccupation with community decline, humiliation, or victimhood”, in which “a mass-based party of committed nationalist militants, working in uneasy but effective collaboration with traditional elites, abandons democratic liberties and pursues with redemptive violence and without ethical or legal constraints goals of internal cleansing and external expansion”. Trump hasn’t abandoned democratic liberties (yet) and is operating within legal constraints (sort of). But he appeared to incite his followers to violence against protesters at his rallies; and his policies on tax-cutting, deregulation, climate change and healthcare reform operate in direct support of the traditional financial Republican elites who – however reluctantly – ended up backing his campaign.

Facebook Twitter Pinterest Conspiracy theory: Steve Bannon. Photograph: Brynn Anderson/AP

Neiwert’s argument that rightwing populism is an essentially cultural rather than economic phenomenon is echoed in Paul Stocker’s book on Brexit, English Uprising. Shorter and less detailed than Neiwert’s book, Stocker’s nonetheless contains a brisk and efficient history of 20th-century British fascism, and how its unlikely postwar re-emergence was enabled by hostility to Commonwealth immigration. Drawing heavily on opinion polls, Stocker blames both press and politicians for fuelling popular racism: from Enoch Powell’s 1968 “rivers of blood” address via Margaret Thatcher’s 1978 “swamping” statement to William Hague’s 2001 “foreign land” speech, in which he referred to restrictions on economic migration. He also shows how a soft version of the conspiracy theory has snaked through government rhetoric on race and culture: from immigration minister James Brokenshire’s claim that immigration primarily benefits “a wealthy metropolitan elite” (but not “the ordinary, hard-working people of this country”) to Theresa May’s 2016 Conservative conference speech, in which she berated politicians with “more in common with international elites than with the people down the road”, concluding famously that “if you believe you’re a citizen of the world, you’re a citizen of nowhere”.

Stocker demonstrates how Ukip represented the “further mainstreaming” of ideas popularised by the BNP; as Nigel Farage boasted: “We have taken a third of the BNP vote from them,” and “I am quite proud of that”.

Neiwert and Stocker are right to question an exclusively economic explanation for rightwing populism. But the lesson of the interwar years is that this populism is successful when nativist cultural movements purport to address the fears of the immiserated. On both sides of the Atlantic, unchecked industrial decline, wage stagnation and personal indebtedness have allowed the politics of racial resentment to flourish.

David Edgar’s adaptation of A Christmas Carol opens at the Royal Shakespeare theatre in Stratford-upon-Avon on 6 December.

• Alt-America: The Rise of the Radical Right in the Age of Trump is published by Verso. To order a copy for £17 (RRP £20) go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.

• To order English Uprising go to www.mhpbooks.com.