James Q. Whitman condemns Trump for his racist statements last week, proposing to bar people from "shithole countries" emigrating to the US, which "hark back to a period in history when Hitler found inspiration" in the US 1924 US Immigration Act. That should "prompt all Americans to remember that Hitler and his fellow Nazis were once big fans of America."

In 1927 Hitler expressed his admiration: “The American Union feels itself to be a Nordic-German state and by no means an international porridge of peoples. This is revealed by its immigration quotas ... Scandinavians … then Englishmen and finally Germans have been accorded the largest contingent.”

The author says, "Trump is a kneejerk authoritarian and a throwback to the old days of white supremacy in America." Indeed, Trump's 2016 election has been widely seen as a factor in the re-energisation of activists and groups in America that celebrate white supremacy. The most infamous racist group - the Ku Klux Klan (KKK) - claims a surge in membership and cross burnings in the Deep South. Some rural areas see high concentrations of extreme race-hate groups with historical links to KKK.

White supremacists reject the social inclusion as endorsed by mainstream political leaders, because they don't want ethnic minorities in America feel valued and important. They rallied behind Trump's anti-immigration agenda during his campaign, after he painted a dark picture of a nation overrun by undocumented immigrants. He wants migrants be chosen upon "merit, skill, and proficiency". And they will also be subject to "ideological certification" to ensure that they love America and its values.

KKK had its roots in the South in 1865. Most of its hate had been towards African-Americans, but it also attacked Catholics, Jews and immigrants. But already "back in 1790, the US Congress revealed its racist outlook by offering naturalization to 'any alien, being a free white person.'” Seeking to boost "white power", KKK often resorted to violence. The first group broke up and does not exist anymore. However, it has regenerated several times in the past 150 years, with other groups formed, bearing the same name and embracing the same ideas. It is the expansion in the 1920s – broadly between the red scare of 1919 to the Immigration Act of 1924 – that provides the most constructive point of comparison with today.

The author says, despite Trump's "denigration of Haiti, El Salvador, and African states as 'shithole' countries," the US is "still a long way from resembling Nazi Germany." But one should not forget that the Nazis' extermination of ethnic groups they deemed inferior, was carried out in the name of eugenics. The Germans were by no means the only advocates of racial purification. Scientists came to the conclusion that Hitler's race hatred was underpinned by the work of American eugenicists. From the turn of the century, German eugenicists formed academic and personal relationships with their American counterparts.

There was deadly violence at a rally in Charlottesville, Virginia last August. Hundreds of white nationalists called to protest against the removal of a statue of a general who had fought for the pro-slavery Confederacy during the Civil War. A woman was killed by a car that was rammed into a crowd protesting the march. The White House defended Trump's reaction after he failed to explicitly condemn far-right groups, that are almost entirely white and male. They put their arms up in Nazi salutes and cheered on the former Grand Wizard of the KKK, David Duke.

The author says: "Looking back, it is important to remember that it was not until the 1965 US Immigration and Nationality Act that the US began to separate itself from the worst aspects of its racist past." Indeed the "Freedom Summer" that saw the killing by the KKK in Mississippi in 1964 of three civil rights workers - who had been working on a project to register African-Americans to vote - shocked the nation and might have helped change America for good. Yet, "as Trump’s presidency makes clear, that past has yet to be permanently overcome."

It would be wrong to take "comfort in the idea that American democracy has not yet been fatally undermined" under Trump. In fact "Americans who love their country should feel sorrow when reading what Hitler said about it in 1928." There is nothing to be proud of having a racist, bigot and know-nothing as president, who doesn't consider anyone non-white and critical of him as his citizens.