“When Fascism comes to America, it will be wrapped in the flag and carrying a cross,” goes a saying that is widely attributed to the first American to win the Nobel Prize for Literature, Sinclair Lewis. In 1935, Lewis wrote a novel called “It Can’t Happen Here,” positing fascism’s rise in the United States. We were taught that fascism was defeated in 1945, with the surrender of Germany and Japan in World War II. Yet the long shadows of that dark era are falling on the presidential campaign trail this year, with eruptions of violence, oaths of loyalty complete with Nazi salutes and, presiding over it all, Republican front-runner Donald Trump.

“Those who cannot remember the past are condemned to repeat it,” the 20th-century philosopher George Santayana wrote. He lived in Europe through both world wars, and witnessed Italian fascism firsthand. Fascism was the violent political movement founded by Benito Mussolini, who took control of Italy in 1922. Mussolini had his political opponents beaten, jailed, tortured and killed, and ruled with an iron fist until he was deposed as Italy surrendered to the Allies in 1943. He was known as “Il Duce,” or “The Leader,” and provided early support to the nascent Nazi movement in Germany as Adolf Hitler rose to power in the 1930s.

Why is this relevant today? It was Donald Trump who recently retweeted one of Mussolini’s quotes: “It is better to live one day as a lion than 100 years as a sheep.” When NBC confronted Trump for retweeting the fascist’s words, he replied, “Sure, it’s OK to know it’s Mussolini. Look, Mussolini was Mussolini. ... It’s a very good quote, it’s a very interesting quote.”

If only the fascist comparisons were limited to his tweets. His rallies have become hotbeds of violent confrontations, consistently fanned by Trump’s heated rhetoric from the podium. After a Black Lives Matter protester was kicked and punched at one of his rallies, Trump said, approvingly, “Maybe he should have been roughed up.” At a rally in Las Vegas in February, after an anti-Trump protester disrupted the event and was escorted out, Trump bellowed: “You know what they used to do to guys like that when they were in a place like this? They’d be carried out on a stretcher, folks.” He went on, “I’d like to punch him in the face, I’ll tell you that.”

Weeks later, a protester was punched in the face at a Trump rally. Rakeem Jones, a 26-year-old African-American man, was being led out of a stadium event by security guards in Fayetteville, North Carolina, when John McGraw, a white Trump supporter, sucker-punched Jones in the face. The local sheriff’s deputies then wrestled the man to the ground -- not McGraw, who threw the punch, but Jones, the victim. The TV program “Inside Edition” interviewed McGraw immediately after the assault. “The next time we see him, we might have to kill him,” McGraw said. He was arrested the next day. Trump has personally pledged to pay the legal defense bills for any rally supporter charged with violence against protesters, including those of McGraw’s. Trump also waffled when asked to disavow the support of the Ku Klux Klan and its onetime Grand Wizard, David Duke.

“Donald Trump shows a rather alarming willingness to use fascist themes and fascist styles. The response this gets, the positive response, is alarming,” said Robert Paxton on the “Democracy Now!” news hour. Considered the father of fascism studies, he is professor emeritus of social science at Columbia University.

Paxton gave a short history of the rise of fascism in Germany: “In the election of 1924, [Hitler] did very poorly, for a marginal party. Then you have the Depression in 1929 and 1930. ... There’s this huge economic crisis with tens of millions unemployed, and there’s also a governmental deadlock. You cannot get any legislation passed.” Paxton continued, “The German Weimar Republic really ceased to function as a republic in 1930, because nothing could be passed. ... So, between 1930 and 1933, President von Hindenburg ruled by decree. And the political elites are desperate to get out of that situation. And here’s Hitler, who has more votes by this time than anybody else. He’s up to 37 percent. He never gets a majority, but he’s up to 37 percent. And they want to bring that into their tent and get a solid mass backing. And so ... they bring him in.”

The partnership that the German elites forged with Hitler and his Nazi Party didn’t work out quite the way they hoped. He took power by subterfuge and by force, arrested and killed his opponents, and plunged Europe into the deadliest war in human history.

Donald Trump is fanning the flames of bigotry and racism. He is exploiting the fears of masses of white, working-class voters who have seen their economic prospects disappear. Should the Republican nominating process end in a contested convention this summer in Cleveland, Trump told CNN Wednesday morning, “I think you’d have riots. I’m representing ... many, many millions of people.”