He's been on the cover of Men's Vogue and editorialized about in Paper, a magazine for wanna-be hipsters. His "look" and his affect -- spare, youthful, unflappable, elegant -- have been compared to John F. Kennedy's.

Suddenly, it seems, everyone is talking about how "cool" Sen. Barack Obama is.

During 2008's breakneck campaign for the presidency, the senator from Illinois has become many things to many people: inspirational leader, dangerously inexperienced, agent of change, cult figure.

Now, though, the "coolness factor" of Mr. Obama's candidacy is being debated with rabid intensity in media circles as he moves steadily, but not yet conclusively, toward the Democratic presidential nomination.

At a photo opportunity last week in a locker room with University of Texas Longhorns football coach Mack Brown, Mr. Obama declined an offer to throw a football for the photographers, noting he'd probably be pretty bad at it.

That was cool, says Ned Martel, deputy editor of Men's Vogue. As a longtime freelance writer, Mr. Martel has covered five presidential campaigns and has occasionally traveled with Mr. Obama during this one.

"He had a communion with the athletes that was very natural," said Mr. Martel. "They were eager to be with him and he had an easy manner around them. I think he just has this effortless self-presentation. He's a little bit academic and a little bit Big Man On Campus."

Most importantly, Mr. Obama's "cool" is unforced, Mr. Martel added, noting that it took a year to persuade him to appear on his magazine's cover in 2006. "What made him a natural subject and ultimately a successful cover is that he let us into his life, he wore his own clothes. He has his look down and I don't think he thinks about it again."

It's not entirely clear what this latest label attached to Mr. Obama really means, though. Is he truly cool or is he just a skinny guy in a too-big suit who happens to be preternaturally comfortable in his own skin?

Asked that question, a lot of ordinarily loquacious political operatives find themselves groping for the right words.

"[Mr. Obama]'s got that thing, that indefinable quality," said Neil Oxman, a Philadelphia-based political consultant. "And it's an amazing thing."

Yes, but what is that "thing"?

"It's when people can't take their eyes off you. There are certain people in the movies you can't stop watching, whether it's Spencer Tracy or Denzel Washington. Obama's got it, too. It's completely natural."

To an unprecedented extent, Mr. Obama has won over many younger voters, and his perceived "cool" -- from his early '60s suits to his United Colors of Benetton multicultural background -- may be a factor in that success, said B.J. Bueno, a branding expert and author of several books on consumer trends.

He's also attracted what is known in marketing circles as "the creatives," people who "are professionally creative for a living, very artistic, who tend to be very skeptical and discerning and probably were not that into politics before now. He's been picked up by the cool generation, and they're giving him great word of mouth. Free advertising, if you will. He's been picked up by the cool group and now he's cool."

In the 2000 book "Cool Rules: Anatomy of an Attitude," British authors Dick Pountain and David Robins deconstructed the meaning of "cool," tracing its roots back to the English author, poet and philosopher Geoffrey Chaucer, and later to a coachman in Charles Dickens' "The Pickwick Papers" who wiped his brow "to show the passengers how cool he is."

Not breaking a sweat: that could apply to Mr. Obama. "He's a very even-tempered person, and he doesn't seem to get rattled," said Alan Colmes, co-host of Fox News Channel's "Hannity & Colmes."

"I think of him as cool the way some jazz is cool. Perhaps over time we'll know the reality, but right now, he seems to be able to take a punch and land one."

Certainly, Mr. Obama has occasionally looked apprehensive in recent debates when Mrs. Clinton went on the offensive, most notably in Cleveland on Tuesday. But when Mrs. Clinton challenged him for merely denouncing but not "rejecting" Nation of Islam head Louis Farrakhan's endorsement, he all but shrugged and said, "I don't see a difference between denouncing and rejecting. But if the word 'reject' Sen. Clinton feels is stronger than the word 'denounce,' then I'm happy to concede the point. And I would reject and denounce."

There are other aspects of "cool," as analyzed by Messrs. Pountain and Robins, that do not seem to describe Mr. Obama: he's not "edgy" cool (hip-hop culture); he's not "rebellious" cool (James Dean, Lenny Bruce). Instead, he's that rarer breed: a cool politician.

"We did claim that since it's inherently narcissistic and individualistic, 'cool' is very uncomfortable with conventional politicians, who by definition have to at least pretend to care about other people," said Mr. Pountain.

Is there anyone else in this campaign who can claim the "cool" mantle for his or herself?

Probably not, says Stuart Fischoff, professor emeritus of media psychology at California State University, Los Angeles.

In their appearances together, "Sen. Clinton looks tense, like she feels the pressure," he said.

And, fairly or unfairly, the camera can be cruel to someone who is not tall and angular, he said. "When you're on camera, it can work against you or for you, and it works in favor of him and not necessarily for her. That sleekness of his adds to his sense of coolness.''

As her campaign has faltered, Mrs. Clinton has been trying on so many different campaign personas, from magnanimous to combative, that voters may have been turned off.

"I call it the Judy Garland problem," Dr. Fischoff said. "On her television show in the 1960s, she trembled a lot and could look uncomfortable, and viewers got so nervous looking at her that the networks dropped her."

John McCain, on the other hand, is definitely not cool.

"He comes across as electrifying, like a high tension wire, which can be interesting but also fatiguing," said Mr. Fischoff. "He looks like a coiled spring and in some sense it's exciting, but you don't ever know if he's going to explode."

Mr. Martel doesn't quite agree.

"McCain is actually kind of cool," he said. "He has the same kind of energy and athleticism to him that Obama has, even for a 71-year-old man. They both know what to do with being the center of attention, in a way Al Gore and John Kerry struggled with. McCain's hotheadedness is there, but during most minutes of his day, he's magnanimous and quick-witted, with a kind of masculine humor that's not quite as biting or juvenile as Bush's towel snapping, but affectionate and a little teasing."

When Bill Clinton appeared on Arsenio Hall in Wayfarer sunglasses playing the saxophone, that was not necessarily cool, "because much of what Bill Clinton presented looked like it was done with effort and calculation. Although 1992 was a very different time," Mr. Martel added.

Mr. Pountain notes, however, that he and his co-author described both Bill Clinton and John F. Kennedy as cool.

"Which meant they lived double lives, professing to care in front of the TV cameras but philandering behind the scenes like something out of 'The Sopranos.'

"As a Brit, I don't know too much about Barack Obama's private life," he added, "but I suspect he's a rather honest and serious man, a bit of an intellectual, perhaps even quote-unquote sincere. And to the extent that he's sincere, he can't be entirely cool. However, he's mastered the appearance of 'cool' sufficiently for young people to identify with him."