He said that, in his opinion, Mr. Trump met the definition of a fascist, would govern like a dictator if allowed, and had no understanding of the Constitution or the concept of rule of law.

He discussed and confirmed previous reports that Mr. Trump had made admiring statements about Hitler, had expressed contempt for disabled veterans and had characterized those who died on the battlefield for the United States as “losers” and “suckers” — comments first reported by The Atlantic.