By Washington correspondent Nick Bryant

There was a moment on Sunday in New Hampshire when I thought that John McCain was going to cry.

The setting was a wood-panelled veterans hall, the type that you get in every small town in New England, which was crammed full of some 300 former soldiers, sailors and airmen.

The Arizona Senator bounded to the stage with his usual Boys Own enthusiasm, his theme tune "Go Johnny Go", fighting its way through a crackly loud speaker.

The normal routine for McCain is to then crack a joke - the one perhaps about how he started this race at minus three in the polls.

Or he might joke that if ever a film is made about his life, he thinks that Tom Cruise should play the title role but that his kids think it should be Danny Devito.

But here in the small, redbrick town of Franklin, his mood was different. He was amongst fellow servicemen and women. He did not need to turn on the charm.

One last mission

"I ask you to join me on one last mission," he said, tightening the grip on his microphone, moving closer to the edge of the stage, "to fight with me shoulder to shoulder. And I promise, my friends, never to lie to you as president."

With that, this small room erupted, the veterans cheering a man whom they regard as an authentic all-American hero, as someone won't let them down.

Mr McCain was visibly moved.

To receive the applause of people he regards as heroes was clearly a moment that touched him.

War hero

For the maverick senator, honour and integrity are hallmark issues, and his personal biography personifies his message.

For five and half years, he was a prisoner of war in Vietnam, refusing early release when his captors discovered he was the son of an admiral.

His story is now a best-selling book, and his candidacy has soared as a result.

Outsider appeal

Mr McCain has had his problems. It is said that he has an explosive temper, and he ended both an unhappy first marriage and a friendship with a corrupt businessmen in the mid-80s who tarnished his reputation.

As a candidate, he is also handicapped by his crusade for campaign finance reform, which has put him at odds with the party leadership.

They are doing everything they can to stop McCain from winning, which is a factor that gives his insurgent campaign much of its appeal.

He is certainly the reportorial favourite. That is to say journalists love him.

He lets us sit on the back of his bus - the Straight-Talk Express - where he is candid, amusing and honest.

How long he will be doing this is the most intriguing aspect of this campaign.

Hard to resist

He has won New Hampshire, but South Carolina is the next big test.

Luckily for him, it is a state with the highest proportion of veterans in the country.

He will be asking them to go on one final mission. It is a plea that they will find difficult to resist.