AMES, Iowa — Donald J. Trump has made his name in politics with provocative statements, but it was not until Saturday, after the flamboyant businessman turned presidential candidate belittled Senator John McCain’s war record, that many Republicans concluded that silence or equivocation about Mr. Trump’s incendiary rhetoric was inadequate.

Mr. Trump upended a Republican presidential forum here, and the race more broadly, by saying of the Arizona senator and former prisoner of war: “He’s not a war hero. He’s a war hero because he was captured. I like people who weren’t captured.”

Mr. McCain, a naval aviator, was shot down during the Vietnam War and held prisoner for more than five years in Hanoi, refusing early release even after being repeatedly beaten.

Mr. Trump and Mr. McCain have been engaged in a war of words over the past week, since the Arizona senator said that Mr. Trump was riling up “crazies” in the party with the inflammatory remarks about illegal immigrants from Mexico.