Rees, who has a long and distinguished record as a film-maker and historian focused on the Hitler era, cites America’s treatment of the Japanese-Americans to make the point that Nazi behaviour was not, and is not, specific to one nation. “The terrible crimes described in this book didn’t so much happen because the Nazis were Germans as because they were human beings.”

In our own times we have seen in Ukraine and the Middle East that many peoples are capable of all-too-describable barbarities against those whom they are propagandised to view as threats or subhumans, not least through the perpetration of conspiracy theories. Amid a torrent of myths that the Nazis propagated, one of the most popular was that Jews masterminded the 1917 Russian Bolshevik Revolution. Lest we forget, 1920s British thrillers penned by Sapper and John Buchan peddled the same thesis.

Ian Kershaw, Hitler’s biographer, applauds The Nazi Mind: Twelve Warnings from History on its cover as “timely, relevant and important”. There is a name missing from Rees’s text, which will nonetheless be in the mind of his every reader, as I am sure it is in Kershaw’s: Trump.

No responsible person will directly compare modern political leaders Hitler or his peers in evil, Stalin and Mao Zedong. Those three were responsible for the deaths of tens of millions of people. Not even the wildest left-wing conspiracists claim that Trump aspires to kill anybody or even that he is antisemitic.

But Trump has indeed threatened to make himself an absolute ruler, with his promise that Americans will not need to vote again. Rees subtitles his book Twelve Warnings from History because by recalling the Nazis he seeks to highlight the techniques that, in the 2020s, we see exploited by the world’s autocrats. The author writes: “It’s often forgotten that dictators frequently do not seize control on their own, instead power is handed to them by others.”

One such technique used by the 1930s tyrants was to generate cults of “us and them”, deluding followers that they were on the side of the afflicted and downtrodden, against elites who patronised and betrayed them. Rees observes that in the wake of the Versailles treaty and economic collapse, “Hitler didn’t just legitimise the anger felt by many of those who listened to him; he also offered hope”.

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After the Second World War the commandant of Gross-Rosen concentration camp, Johannes Hassebroek, said: “I was full of gratitude to the SS for the intellectual guidance it gave me … Many of us had been so bewildered … We did not understand what was happening around us, everything was so mixed up. The SS offered us a series of simple ideas that we could understand.”

Another SS veteran who Rees interviewed in the 1990s testified, like many such people I have met, that the Hitler era was a joyous time. “Germany was on the up, otherwise Churchill wouldn’t have wanted to fight us, would he? … What stood against us, against the Reich, was the whole world. So you defend yourself against it.”

The same man, Bernd Linn, dismissed the idea that the Holocaust had been a unique horror. “No! Absolutely not! Let everyone wash their own dirty linen, then England will have enough to do, more than enough, the French too, the Dutch — look at all their colonies.”

Tyrants need enemies so that they can cast themselves and their followers as victims. In a 1940 essay on Mein Kampf, George Orwell wrote that “Hitler could not have succeeded against his many rivals if it had not been for the attraction of his own personality …. He is the martyr, the victim, Prometheus chained to the rock, the self-sacrificing hero who fights single-handed against impossible odds. If he were killing a mouse, he would know how to make it seem like a dragon.” Although few non-Republicans doubt that Trump is a lawbreaker, it proved counterproductive to indict him because this fed the myth of himself as a persecuted hero.

Japanese-American children waiting to be relocated in 1942

CORBIS/GETTY IMAGES

Despite vilifying them, Hitler enlisted the support of elites, and above all rich bankers and industrialists — partly because of their overarching fear of communists who would take away their money and partly because they fooled themselves that they could exploit him.

Around the world some intelligent and educated people endorsed fascism. The British establishment backed Franco in Spain and Mussolini in Italy for more than a decade, just as today the richest Americans fawn over Trump, indifferent to his reckless policies on almost everything save tax cuts. The Catholic church backed Spain’s Franco and indulged Hitler, just as today the Russian Orthodox church supports the murderous Vladimir Putin.

The world is complicated. We should trust no one who offers simple solutions to anything — think Nigel Farage. But to maunder about hard choices, for instance about immigration, is a pitiful response to voters craving deliverance by an apparently plausible saviour. Look at the radiance in the faces of many of those attending Trump rallies. And be afraid.

Rees, an expert on the Nazi period, focuses on recalling its hideous highlights and devotes only a few concluding pages to reflections. He leaves his readers to draw the conclusions and make the comparisons. Some will regret his caution about making explicit what is implicit throughout his guide to the Nazi chamber of horrors.

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In our anxiety not to succumb to hyperbole, we hesitate to say aloud that Trump’s declared commitment to corrupt or destroy great institutions of democracy by politicising their staffing threatens democracy’s very existence. Thus we fail to sound the tocsin as it ought to be sounded.

The great Dresden diarist Victor Klemperer wrote in March 1933: “It is shocking how day after day naked acts of violence, breaches of the law, barbaric opinions appear quite undisguised as official decree.” What would Klemperer say today about the US president-to-be’s proclaimed intent to pardon the 2021 Capitol insurgents, his daily stream of untruths?

Rees raises the question: what might the US general charged in 1942 with rounding up 110,000 Japanese-Americans have done with those people had he wielded the kind of unrestrained authority possessed by the Nazi government?

He concludes: “The reason why that is the right question to ask is that it reminds us that it was ultimately the political structures in America that held [the general] back. It wasn’t one individual hero, fighting against the odds, but the system.” And the system — the bureaucracies of state — is what Trump is pledged to attack, and even to destroy, probably with the aid of a US Supreme Court and Congress already frighteningly warped to his will.

The Nazi Mind: Twelve Warnings from History by Laurence Rees (Viking £25 pp448). To order a copy go to timesbookshop.co.uk. Free UK standard P&P on orders over £25. Special discount available for Times+ members