McCain also took Obama to task for statements made Sunday by retired Gen. Wesley Clark, an Obama supporter, denying that McCain's war record should be considered a qualification to be president.
Asked about Clark's comments on the campaign plane, McCain snapped, "I think it's up to Sen. Obama now not only to repudiate him, but to cut him loose."
Asked how his experience in Vietnam prepares him for the presidency, McCain grew visibly upset.
"Please," he said.
Then, after taking a few moments to compose himself, McCain said, "In the prison camps of North Vietnam, there weren't Republicans or Democrats -- there was patriots, and I had the great honor of serving with them, and that's a memory I'll always cherish."
Unusual as it has been so far, the trip plays to some of McCain's strengths.
Foreign policy is one of the few areas where he holds an advantage over Obama -- a full 6 points in public opinion, according to an ABC News/Washington Post poll.
The Arizona senator hopes this trip will reinforce that lead, and keep it front and center in the minds of voters back home.
In the United States, McCain's self-described "underdog" campaign underwent a shake-up today when veteran Republican operative Steve Schmidt was put in charge of day-to-day campaign operations.
Campaign manager Rick Davis keeps his title but will now focus more on general strategy and long-term strategic planning, according to campaign officials and other Republicans familiar with the move.
Although Schmidt has had a major role with the McCain campaign since December, the shake-up will leave an experienced and respected operative with more responsibility over scheduling, agenda-setting and efforts to define both McCain and Obama.
"Organized, focused, and strategic -- what's not to love?" one Republican with close ties to the McCain campaign told ABC News. "I think it will help."
ABC News' Rick Klein, Karen Travers, Brett Hovell, Ursula Fahy and Maria Ines Carrizosa contributed to this report.