DENVER (AP) — John McCain was in his favorite campaign setting, a town hall meeting, when he spotted a promising target. ‘‘I’d love to recognize you first, sir,’’ the Republican presidential candidate said to a man in a Vietnam War veteran’s hat.

Instead of a softball opening question from a fellow vet, however, McCain got a lengthy harangue, as the man insisted the senator had opposed better medical benefits for veterans.

McCain, who spent more than five years as a prisoner of war, politely said the man was mistaken. He finally broke it off, saying, ‘‘I’ll be glad to examine what your version of my record is.’’

The July 7 episode in Denver underscored the iffy nature of a campaign strategy that McCain seems to adore. Town hall sessions — in which he makes opening remarks and takes questions for an hour or more — have become McCain’s staple, and he constantly needles Democratic opponent Barack Obama for not joining him onstage.