Republican Sen. John McCain heads into the first of the presidential debates Friday with a track record as a scrappy combatant and the instincts of a fighter pilot prepared to take out his opponent and willing to take risks to do so. He has used fairly consistent techniques.

During his roughly 30 debates on the national stage, he has been an aggressive competitor who scolds his opponents, grins when he scores and is handy with the rhetorical shiv.

A review of several of McCain's debates shows that he is most comfortable and authentic when the subject is foreign policy. And in a stroke of good fortune, foreign policy is the topic for Friday, the first of three 90-minute debates with Sen. Barack Obama.

Bedrock of his experience

Voters give higher marks to McCain as a potential commander in chief, and Obama should expect McCain to question his credentials for the job at every turn.

McCain is likely to steer the conversation to his captivity in Vietnam. It's the bedrock experience of his life and is the organizing principle of his political identity.

He showcased it most triumphantly last October in a debate in Orlando, Fla. The moderator noted that while McCain had strongly supported the troop surge in Iraq, Sen. Hillary Rodham Clinton, then the likely Democratic nominee, wanted to pull the troops out. McCain was asked whether the surge was a winning issue for Republicans in 2008. With a quick nod to the troops, McCain, characteristically, hijacked the question and skipped to pork-barrel spending, his favorite bête noire.

"In case you missed it a few days ago, Senator Clinton tried to spend $1 million on the Woodstock Concert Museum," McCain said slyly. "Now, my friends, I wasn't there," he continued, letting it sink in why he had missed that '60s be-in.

"I'm sure it was a cultural and pharmaceutical event," he deadpanned. "I was tied up at the time."

The audience roared with approval and rose to its feet for an extended ovation.

Most of McCain's moments on the debate stage are rarely that dramatic, but they are not without flair. He uses short, active verbs that project strength, and he can connect with audiences on a visceral level using down-to-earth language. He was one of 10 Republicans on stage when the primary debates began in May 2007, but he managed to stand out with one vivid remark. Saying he would do "whatever is necessary" to capture Osama bin Laden, he declared, "I'll follow him to the gates of hell."

But that debate also showed that McCain's performances could be uneven. He stumbled over some words. He looked confused at several junctures and was slow on the draw, retrieving his time on occasion to amend earlier answers.

His weakness: looking wooden

When the topic strays from foreign policy, McCain's interest can fade and he can lapse into his stump speech.

"McCain's major weakness is looking wooden, and when he's out of his comfort zone, his sound bites become weaker and his evasions of questions become more obvious," said David Lanoue, a political scientist at the University of Alabama and an expert in presidential debates.

What lasts from a review of McCain's national debates is that he relishes confrontation. He presents himself as the authority on the broad themes of war and peace, life and death.

David Birdsell, who specializes in presidential debates at Baruch College, said McCain could be "irascible and pugnacious and clearly stoked by personal animosity." It will be a challenge for him to keep that side in check, Birdsell said.