Racial theories that were thought consigned to the dustbin of history after they fuelled the horrors of the Holocaust have been given a fresh platform by US president Donald Trump, who learned them on his father's knee.
With racial tensions in the US at the lowest point in a generation, Trump spoke to a crowd of his supporters last week in Minnesota, a state with an overwhelmingly white population - but one that has seen a recent increase in the immigration of people of colour.
It should have been a remarkable speech, with Trump wildly veering between sharing conspiracy theories about his political opponents, taking snide jabs at immigrants and celebrating armed police taking action against members of the media.
But Trump delivered it all in seeming ignorance of the death of Ruth Bader Ginsburg - despite members of the crowd trying to shout the news at him - and that quickly became the headline.
The rhetoric was also nothing new from the president, who has been widely criticised in the past for his flirtations with white supremacists and his tacit support for conspiracy theorists.
Earlier in the speech, Trump played on the fears of his nearly all-white crowd, telling them: "Every family in Minnesota needs to know about sleepy Joe Biden's extreme plan to flood your state with an influx of refugees from Somalia, from other places all over the planet."
He also targeted Minnesota congresswoman Ilhan Omar, a Somali refugee who has previously described Trump as a "xenophobic, racist tyrant", by repeating discredited claims that she had married her own brother.
Then, drawing together the threads, he praised the assembled white crowd for their "good genes", gleefully espousing racial theories that still hold currency for white supremacists long after they spawned genocide on a massive scale.
"You have good genes, you know that right?" Trump said to to a ripple of applause.
"A lot of it is about the genes, isn't it? Don't you believe? The racehorse theory," he added.
"You think we're so different? You have good genes in Minnesota."
What Trump was saying, that "good" genes can be the "right" genes, is the basis for eugenics - the theory that selective breeding can improve the human race.
That theory had another infamous supporter last century, and Hitler's rapid dedication to it saw the deaths of millions in the Holocaust.
The comparison wasn't lost on many, with historian Steve Silberman saying the rhetoric used by Trump was "indistinguishable" from that used by the Nazis.
Trump's racist cheerleading in the speech made plain what has been suggested before, that he views himself as superior - a "very stable genius" - because he believes he has "good genes".
"I have Ivy League education, smart guy, good genes. I have great genes and all that stuff, which I'm a believer in," Trump said in 2016.
In 2010 he told CNN he was a "gene believer".
"Hey, when you connect two racehorses, you usually end up with a fast horse," he said.
"And I really was - you know, I had a - a good gene pool from the standpoint of that."
In 2016, a documentary revealed that Trump learned the racehorse theory at an early age.
In the film, Trump biographer Michael D'Antonio was asked about the theories supported by Trump's father Fred, the son of a German immigrant.
"Fred had theories. He shared them with his kids. Donald especially liked one of them," the narrator said.
D'Antonio replied: "This is a very deep part of the Trump story. The family subscribes to a racehorse theory of human development, that they believe that there are superior people, and that if you put together the genes of a superior woman and a superior man, you get superior offspring."