McCain, however, can't risk turning off undecided swing voters, many of whom recoil at negative campaigning.

Early on in his 50-minute address, protesters inside the hall interrupted McCain's address a few times, but on each occasion the crowd shouted them down with chants of "USA, USA." McCain himself was unfazed, telling the audience, "please don't be diverted by the ground noise and the static."

"Americans want us to stop yelling at each other," he added, trying to use the disruption to his advantage.

A Vietnam prisoner of war, McCain pointed to his 5 1/2 years in captivity as a life-changing turning point.

"I fell in love with my country when I was a prisoner in someone else's," he said. "I loved it because it was not just a place, but an idea, a cause worth fighting for. I was never the same again. I wasn't my own man anymore. I was my country's."