The 83-year-old Israeli-American writer, who escaped the Nazis by being hidden in a Catholic boarding school in France, described Trump as a "dangerous crazy".
He said the controversial Republican candidate could win November's election because of Hillary Clinton's "tendency to lie and to hide things".
"One cannot exclude Donald Trump winning even though he is a dangerous crazy," he told AFP.
"He says whatever comes into his mind."
Friedlander's magisterial two-volume history of Nazi Germany and the Jews charts Adolf Hitler's rise to power in a period where populism was rising across the world as it is today.
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"At the same time, there is a huge swathe of Americans, mostly poor, angry whites, who dream of having him in the White House.
"He is kind of a release valve for their anger against the 'establishment' represented by Barack Obama and Hillary Clinton.
"Because she has, unfortunately, a tendency to lie and to hide things," he said, referring to her recent bout of pneumonia, which her campaign was only forced to disclose after she was seen stumbling into her car.
Friedlander, who is based in Los Angeles, also warned of the rise of anti-Semitism and of Holocaust denial.
"Negationists are, in general, anti-Semites, and I am utterly opposed to debating with them. It gets you nowhere, they will always find a so-called detail showing that all these stories of gas chambers were a joke.
"They are obsessed by the idea that Jews could have invented the story of their extermination," said the author, whose new books, "Reflections on Nazism" and "Where Memory Leads", have just been published in France.