Like many of the others, Mr. Burns said he heard echoes of dangerous populist demagogues in Mr. Trump’s rhetoric. Among the issues that were cited were his calls to ban all Muslims, his characterization of many Mexicans as criminals and his mockery of veterans and people with disabilities. Mr. Trump has said that the country faces crises that require strong action to protect its borders, and that his role as an outsider has cost him the approval of elites and entrenched interests, including in his own party.

In the 1920s, fear of immigrants fueled the rise of the Ku Klux Klan and exclusionary laws aimed at European Catholics and Asians, said Ms. Ruiz, a professor of history at the University of California, Irvine, and past president of the American Historical Association. Also, about one-third of the Mexican population in this country was pushed out, more than half of them United States citizens by birth, she said.

“Playing with hate has had tragic consequences throughout our history,” she said.

Mr. Chernow, a Pulitzer Prize winner whose “Alexander Hamilton” was a principal source for the Broadway musical “Hamilton,” said he had been struck by Mr. Trump’s lack of reference to the founding documents of American history, or to presidents like George Washington, Abraham Lincoln and Franklin D. Roosevelt. “The only historical movement that Mr. Trump alludes to is a shameful one — ‘America First,’” Mr. Chernow said, recalling an isolationist political organization at the time Nazi Germany was taking power across Europe.

Mr. Lewis, a professor at New York University and biographer of W. E. B. DuBois, recalled Wendell Willkie, a presidential candidate with a superficial resemblance to Mr. Trump, in that he was a wealthy businessman who had held no prior electoral office and became a Republican just shortly before the 1940 campaign against Roosevelt. But after the election, Willkie distinguished himself by calling for a loyal opposition, Professor Lewis said. (Willkie served as Roosevelt’s informal emissary to Britain, in a sign of bipartisanship.) “For Donald Trump, Willkie’s loyal opposition concept is surely anathema,” Professor Lewis said.

Mr. Leuchtenburg, a professor emeritus at the University of North Carolina at Chapel Hill and a leading scholar of the American presidency, said Mr. Trump was essentially ahistorical. “He has no sense of the American past,” Professor Leuchtenburg said. “He doesn’t understand the achievements of this country.”