Footage has been discovered showing 20,000 people cheering on the idea of a white supremacist USA in New York's Madison Square Garden - in the guise of a "pro-American rally".
The footage, shot on February 20, 1939, shows the audience throwing Nazi salutes as the American flag is carried to a stage bedecked with a 30-foot-high painting of George Washington flanked by swastikas.
The Pledge of Allegiance is then read out before the group's leader, German-American Fritz Kuhn, gets up to denounce the "Jewish media" and call for America to be "returned to the American people ... a white, gentile-ruled United States".
August's Unite the Right rally in Charlottesville, which saw Nazis openly chanting about Jews and assaulting counter-protesters, seemed to some like an aberration in modern America.
But the seven-minute clip, compiled by Oscar-nominated documentary filmmaker Marshall Curry for Field Of Vision, shows an even larger gathering - in New York, which even in the 1930s was considered a liberal bastion.
Curry edited together the clips from fragments showing unrest outside Madison Square Garden, while inside Kuhn spouts anti-Semitic rhetoric.
The rally is interrupted when Isadore Greenbaum, a 26-year-old Jewish plumber's helper from Brooklyn, rushes the stage.
He's then thrown to the crowd and beaten by a group of fascists before the police arrive to haul him off. He was stripped of his trousers, Curry said.
The NYPD arrested him for disorderly conduct and fined $25 ($431 today).
The clip ends with the crowd standing for the Star-Spangled Banner, and text noting that Hitler was building his sixth concentration camp at the time.
"A friend of mine told me about it last year, and I could't believe that I'd never heard of it," Curry said of the rally, according to Field Of Vision.
"When I found out it had been filmed, I asked an archival researcher, Rich Remsberg, to see what he could find."
Curry continued: "So he gathered it, and I edited it together into a short narrative. When Charlottesville happened, it began to feel urgent."
The event was hosted by the German American Bund, which had training camps in upstate New York, as well as New Jersey, Pennsylvania and Wisconsin - and which was terrifyingly popular in the US at the time.
But despite the thick accents sported by Kuhn and his cronies, the gatherings were presented as "pro American rallies".
Indeed, those very words are seen on the sign outside the building, along with more mundane events: "Hockey Tues night, Rangers vs Detroit; Basketball Wed night, Fordham vs Pittsburgh."
And at the time - when Hitler's persecution of the Jews in Europe was well known, but before the full horror of concentration camps had been revealed - these attitudes were not uncommon.
"In a part of Fritz Kuhn's speech that isn't in the film, he applauds Father Coughlin, whose radio shows praising Hitler and Mussolini reached audiences of 30 million," Curry said.
"Henry Ford and Charles Lindberg expressed anti-Semitic beliefs.
"And press magnate William Randolph Hearst declared, 'Whenever you hear a prominent American called a fascist, you can usually make up your mind that the man is simply a loyal citizen who stands for Americanism'."
Perhaps with that in mind, Curry invoked a quote from Halford E Luccock, a New York Times reporter of the period.
The reporter wrote: "When and if fascism comes to America it will not be labeled 'made in Germany'; it will not be marked with a swastika; it will not even be called fascism; it will be called, of course, 'Americanism'."
"To me, the most striking and upsetting part of the film is not the anti-Semitism of the main speaker or even the violence of his storm-troopers," Curry said.
"What bothers me more is the reaction of the crowd. Twenty-thousand New Yorkers who loved their kids and were probably nice to their neighbours, came home from work that day, dressed up in suits and skirts, and went out to cheer and laugh and sing as a speaker dehumanised people who would be murdered by the millions in the next few years.
"This point is less an indictment of bad things that Americans have done in the past, than it is a cautionary tale about the bad things that we might do in the future."
Curry makes no bones about comparing Kuhn to President Donald Trump, whose own rallies had attracted support from fascist members, as well as the more mainstream American right.
"It really illustrated that the tactics of demagogues have been the same throughout the ages," he said.
"They attack the press, using sarcasm and humor. They tell their followers that they are the true Americans (or Germans or Spartans or...).
"And they encourage their followers to 'take their country back' from whatever minority group has ruined it."
Kuhn was arrested for embezzling the German American Bund's money and imprisoned in December 1939.
He was stripped of US citizenship in 1943 and deported to West Germany in 1945, at the close of the Second World War - by which point the US was grateful to forget its open flirtation with fascism.
"In the end, America pulled away from the cliff, but this rally is a reminder that things didn't have to work out that way," Curry said.
"If Roosevelt weren't President, if Japan hadn't attacked, is it possible we would have skated through without joining the war?
"And if Nazis hadn't killed American soldiers, is it possible that their philosophy wouldn't have become so taboo here?"