“I’m calling, very simply, for a shutdown of Muslims entering the United States,” Donald J. Trump said on Dec. 8, 2015. It was early in his presidential campaign, and he was saying that sort of thing all the time.

On this occasion, though, he also cited a historical precedent.

“Take a look at what F.D.R. did many years ago,” Mr. Trump said. “He did the same thing.”

President Franklin D. Roosevelt signed a 1942 executive order that sent more than 110,000 people of Japanese ancestry to internment camps.