When Donald Trump shared a video that dreamed of a “unified reich” if he wins the US presidential election, and took nearly a full day to remove it, the most shocking thing was how unshocking it was.

Trump has reportedly said before that Adolf Hitler did “some good things”, echoed the Nazi dictator by calling his political opponents “vermin” and saying immigrants are “poisoning the blood of our country”, and responded to a white supremacist march in Charlottesville by claiming that there were “very fine people on both sides”.

The Hitler-Trump analogy is controversial. “Some of Trump’s critics – including Biden’s campaign – argue that Trump’s incendiary rhetoric and authoritarian behavior justify the comparison,” the Politico website observed recently. “Meanwhile, Trump’s defenders – and even some of his more historically-minded critics – argue that the comparison is ahistorical; that he’s not a true fascist.”

The former camp now includes Henk de Berg, a professor of German at the University of Sheffield in Britain. The Dutchman, whose previous books include Freud’s Theory and Its Use in Literary and Cultural Studies, has just published Trump and Hitler: A Comparative Study in Lying.

In it, De Berg compares and contrasts Hitler and Trump as political performance artists and how they connect with their respective audiences. He examines the two men’s work ethic, management style and narcissism, as well as quirks such as Hitler’s toothbrush moustache and Trump’s implausible blond hair.

In a Zoom interview from his office at the university campus, De Berg quotes the American comedian and actor George Burns: “The most important thing in acting is honesty. If you can fake that, you’ve got it made.” He adds: “The most important thing in populism is authenticity. The moment you’re able to fake that, you’re in.”

De Berg, 60, happened to be renewing his study of National Socialism, and rereading Hitler’s autobiographical manifesto Mein Kampf, just as Trump was first running for the White House in 2015. “Obviously, there are massive differences,” he acknowledges. “Hitler was an ideologically committed antisemite who instigated the second world war and was responsible for the Holocaust in which 6 million Jews died.

“But then I looked at their rhetorical strategies and their public relations operations and I began to see how similar they are in many ways. So I thought, OK, why not do a book looking at Hitler from the perspective of Trump?

“We tend to see Hitler as a genocidal mass murderer, which of course he was, but not so much as a populist. I thought looking at it through the perspective of Trump can help us wrap our heads around the idea as to why so many people actually supported Hitler and vice versa.”

Above all, De Berg argues, Hitler and Trump were and are political performance artists who speak only vaguely about policies – Make Germany/America great again – but know how to draw attention using jokes, insults and extreme language. In this they differ from Joseph Stalin, the Soviet autocrat who was a poor public speaker and preferred to work behind the scenes.

“Their extremist statements are very deliberately meant to provoke a reaction and to get them into the press. Hitler actually writes quite openly about this in Mein Kampf and this of course is the challenge: what do you then do as a journalist or as an opposing political party when the other person makes these extreme statements?

“Do you then not report these things, but then the populists will say whatever they want to say? Or do you contradict them and point out the lies and the extremism, but in that way you’re only drawing more attention to the fact that they’re running and to all they’re proposing?”

Along with its headline-grabbing potential, the extremist language also plays well with many voters. De Berg says: “Most of their electorate are dissatisfied with the status quo for a variety of reasons – globalisation, automation – so they want to change the system and here you have an anti-establishment candidate who is not politically correct, who says that we will sort it, who doesn’t come up with all these ‘cowardly, rotten compromises’.”

Many such voters are ready to blame a scapegoat, “the other”. Hitler blamed Jews for Germany’s defeat in the first world war; Trump launched his 2015 campaign demonising immigrants from Mexico and continues to put border security front and centre. “It decomplexifies the world. Instead of abstract social structures and historical developments, you have one specific group of people that you can blame all your problems on.”

One of the touchstone observations from the early Trump years came from the journalist Salena Zito. In September 2016 she wrote in a column for the Atlantic magazine that “the press takes him literally, but not seriously; his supporters take him seriously, but not literally”.

Again De Berg is alive to rhymes with Hitler. “There were a lot of National Socialists interviewed after the war who said, well, yeah, OK, Hitler was saying all these extreme things but we realised he was a mass politician and we thought that he was just saying things that he didn’t really mean, that he was just exaggerating a little bit. Someone said the demands in Mein Kampf we took as the dogmas in the Bible – no one thought that these things would be fulfilled 100%.

“The same is true, dangerously, with the things that Trump says. In his rallies he outlined a whole range of very problematic things that he would do when he was going to be president, but that doesn’t mean all people literally believe that. I don’t think they literally believed that he was going to build this big concrete wall between Mexico and the United States. Many of them thought, unconsciously, what he’s really saying is he will protect America’s traditional identity.

“And that – to use a posh phrase – interpretative openness means that both the more extreme followers and the less extreme or ‘moderate’ followers can recognise themselves in the speaker’s words. That made Hitler and makes Trump so difficult.”

Trump’s incoherent, meandering and zigzagging mode of speech adds to the effect. “Trump goes from the FBI to a judge to the Democrats to communists and so on. You can then say, well, clearly this guy is an intellectual nitwit, he can’t talk in a logical, argumentative way. He could but he realises that this vague way of tying all these people together actually gives different sections of the electorate different things they can identify with. Some might not like the FBI, others might not like immigrants and so on.”

Trump made more than 30,000 false or misleading claims during his four years as president, according to a count by the Washington Post. Perhaps the most egregious is “the big lie” that he, not Joe Biden, won the 2020 presidential election, only for it to be stolen due to widespread fraud. De Berg writes in his book: “The idea behind the concept of the big lie is that if an untruth is sufficiently extreme, people are likely to accept it if only because they cannot bring themselves to believe that anyone could lie in such an outrageous manner.

“It was Hitler who came up with the concept, writing in Mein Kampf that ‘the great masses of the people … more easily fall victim to a big lie [große Lüge] than to a little one, since they themselves lie in little things, but would be ashamed of lies that were too big. Such a falsehood will never enter their heads, and they will not be able to believe in the possibility of such monstrous effrontery and infamous misrepresentation in others.’”

The spectacle and social glue of mass rallies is also key. In controversial comments to Playboy magazine, the British singer David Bowie once observed: “Adolf Hitler was one of the first rock stars … Look at some of his films and see how he moved. I think he was quite as good as Jagger. It’s astounding. And boy, when he hit that stage, he worked an audience. Good God! He was no politician. He was a media artist. He used politics and theatrics and created this thing that governed and controlled the show for 12 years. The world will never see his like again.”

Trump’s rallies are typically rollicking affairs, the atmosphere part circus, part concert, part sports, bringing like-minded people together as ritualistically as church. In all weathers they share a collective sense of grievance and also find ways to have fun. In small towns that often feel left behind by big cities, they can represent the biggest event of the year and offer the thrill of live performance in an otherwise digitally saturated age.

De Berg comments: “If you look at the lives of many ordinary Germans during the Weimar Republic immediately after the first world war, when the economy wasn’t doing well and there were all sorts of problems, many of them could not afford to enjoy all sorts of spectacles but they could go to a Hitler rally.

“You can go to a Trump rally as well and that creates a feeling of solidarity, a community of feeling, which of course is at the same time the dangerous thing because people then identify with each other. They lose their individuality, they lose their critical capacity, and at the same time all together they identify with a political leader, so the political leader can do whatever he wants.”

There is also something alarmingly familiar about the way in which the Republican party thought it could co-opt and control Trump, only to find itself capitulating and being recast in his image. One by one the party stalwarts have fallen into line, abandoning long-held principles, while dissenters have been purged.

De Berg continues: “Hitler goes from 2.6% of the vote in 1928, meaning more than 97% of the electorate don’t want him, to the Nazi party becoming the biggest party in 1932. Then these conservative politicians say, OK, we’ve got this political nincompoop here but he’s a populist and he’s popular, the people like him. If we try and make this guy vice-chancellor then he can do our bidding.

“Hitler says no, I’m not going to be vice-chancellor, I want to be chancellor, so eventually they give in but they still think that he is going to do what they want and push through their policies. One of these conservative politicians memorably said, ‘We’ve hired him.’ Hitler manipulated them and he becomes chancellor and from there on in it all goes disastrously wrong with German society.”

He adds: “One of the most worrying things for me about Trumpism is the way he has managed to transform what you thought were very rightwing but ultimately rational politicians into people who have become basically Trumpists.

“What happened was not that they manipulated Trump but Trump ended up manipulating them and then, in effect, just taking over the Republican party. All these people had to renounce all the things they used to believe in: international free trade agreements, a forward-leaning role for America in the world.”

There is, the academic warns, method in Trump’s madness: the buffoonery, chaos and word salad speeches may be more calculated than they appear. “I would like people to become more aware of how incredibly consciously Trump is going about doing what he’s doing, how incredibly cunning and devious he’s been. People should absolutely not underestimate this guy.”