McCain was born in the Panama Canal Zone, became famous as a Vietnam prisoner of war and has spent his long Senate career traveling to more foreign countries than most people could even name.
He makes his eighth trip to Iraq this weekend, a visit sure to get a lot of attention. But his weeklong overseas trip also includes Israel, Britain and France - all countries where he's made many visits.
A defiant supporter of the 2003 invasion and President Bush's troop increase last year, McCain is likely to focus in Iraq on the drop in sectarian violence and U.S. and civilian casualties since last summer.
His own situation has changed strikingly, too, since then. Now he's the Republican presidential nominee-in-waiting.
Last April, as McCain's chances for winning the nomination seemed uncertain, the four-term Arizona senator toured a Baghdad marketplace, hailing the progress even though he was protected by three Black Hawk helicopters, two Apache gunships and 100 U.S. troops.
He was widely ridiculed as being out of touch.
As he returns, a new Pentagon study shows sectarian violence down 90 percent and U.S. and civilian casualties down 70 percent since last July.
Last December, nearly two-thirds of Americans said they opposed the war, including nearly a third of Republicans and nearly all Democrats, according to an Associated Press-Yahoo News poll. Opinions on the war have remained basically steady.
However, a poll released Friday by NBC News and The Wall Street Journal said about 35 percent of those questioned think McCain has the right approach for Iraq, compared with 30 percent forand 27 percent for .
McCain calls the fight against Islamic extremism the "transcendent challenge of the 21st century."
"I've made it abundantly clear that I would much rather lose a campaign than a war," he said this week in New Hampshire.
The one may be tied to the other.
Says Michael O'Hanlon, a foreign policy analyst at the Brookings Institution: "I have a hard time seeing how he wins if Iraq falls apart between now and November, and I have a hard time seeing how the Democrats use Iraq against him over that time if things continue to improve."
As Democrats Clinton and Obama fight over which of them has the credentials to be the next commander in chief, McCain offers a much lengthier foreign policy and military resume.
Now 71, he was born in the Canal Zone, where his father, a naval officer, was stationed. A graduate of the Naval Academy, McCain flew in Vietnam and was a prisoner of war for more than five years. In the Senate, he is the senior Republican on the Armed Services Committee.
He has visited every region of the world, including Antarctica and the Arctic Circle, and frequently meets with leaders of the countries to which he's traveled, both when he visits their countries and when they visit the United States.
McCain has been across the world so many times that aides named off the tops of their heads some 69 countries he's visited - including Azerbaijan, Estonia, Laos and Palau - and warned the list was far from exhaustive.
Aides say he keeps up to speed on the politics and policies of many nations - a passion he regularly displays to reporters traveling with him - and understands the long-term ramifications of having well-established personal relationships with foreign leaders.
He makes it a point to meet with up-and-comers, too. Aides say he met Angela Merkel at a Munich conference several years ago before she became German chancellor. In summer 2004, McCain met at a restaurant with Viktor Yushchenko before the Orange Revolution when he was elected Ukrainian president.
Next week, McCain is expected to meet with British Prime Minister Gordon Brown for the first time, and French President Nicolas Sarkozy for the third time. He met and corresponded with Sarkozy both before and after he was elected. The two last saw each other last summer.
McCain has relationships with every leader in Israel he plans to see, including Prime Minister Ehud Olmert, Foreign Minister Tzipi Livni, Defense Minister Ehud Barak and hawkish opposition leader Benjamin Netanyahu.
The senator last met with Iraqi Prime Minister Nouri al-Maliki last Thanksgiving, and he's also gotten to know other members of the Iraqi government.
He returns with two of his chief presidential supporters, Sens. Joe Lieberman of Connecticut and Lindsey Graham of South Carolina, but he insists it is a fact-finding venture, not a campaign photo opportunity.
"There's nothing like being on the ground," he said. Mentioning a mountainous area in northwestern Pakistan, he added, "I went to Waziristan once and it gave me a much better understanding of how difficult it is to get Osama bin Laden."
O'Hanlon, the Brookings analyst who says he's a Democrat, says McCain has shown a more realistic vision than Bush about the number of troops needed to succeed in Iraq, as well as the problems that were likely to be encountered after the invasion.
"What that tells me in terms of future policy is McCain may be willing to stay the course, so to speak, in terms of future difficulties, but also assess if the strategy is really working or not," O'Hanlon said.
Jon Alterman, a former Bush administration aide who now runs the Middle East program at the Center for Strategic and International Studies, notes that Bush's father spoke of "the vision thing."
"This president has always been strong on the vision thing, even when the implementation is lacking. I don't think John McCain is enamored with the vision thing. He talks about the task and focuses on the task. It's just a different orientation," Alterman said.
"The straight talk express is not often associated with diplomacy," he said. "But the advantage of it is you know what you're getting. And it may be that he's able to form quite valuable relationships precisely because of his bluntness."