Throughout his campaign, Donald J. Trump has flouted official histories and facts, claiming, for example, that thousands of Muslims celebrated in New Jersey on Sept. 11, and that the Department of Labor cooks the unemployment books and the real jobless rate is 23 percent. 

On Friday night, Mr. Trump embraced another urban legend, claiming that an American general a century ago summarily executed terrorists with bullets dipped in pig’s blood. He presented it as an example of how brutal toughness toward terrorists was the way to safeguard the United States.

“This is something you can read in the history books,’’ Mr. Trump said, adding, “Not a lot of history books, because they don’t like teaching it.’’

In the early 1900s, he recounted, Gen. John J. Pershing, known as Black Jack, captured 50 terrorists, dipped 50 bullets in pigs’ blood and had his soldiers execute 49 of the men. “The 50th person, he said, ‘You go back to your people and you tell them what happened,’ ’’ Mr. Trump said. “And for 25 years there wasn’t a problem.’’