The gum-chewing man in the purple sports jacket and black suede shoes is all but hidden in the crowd around George W. Bush, a battered Honeywell camera around his neck the only clue that he might be more than a mere onlooker.

Every few moments, Mark McKinnon raises the 8mm camera here in the basement of Sisulu Children's Academy in Harlem, capturing Bush smiling at the assembled group of second-graders, or tilting his head in a Reaganesque way, or intoning that "no child should be trapped in a failing school."

In the next few weeks, such snippets will become part of a Bush advertising blitz that will attempt to raise the country's comfort level with the Republican presidential front-runner. But more interesting than the commercials themselves is the unorthodox choice of the media adviser who is making them.

McKinnon is a former teenage runaway, onetime songwriter for Kris Kristofferson, erstwhile folk rock singer and temporary jailbird. Even more unusual in the fiercely partisan world of national politics, he is a lifelong Democrat. And in a sense, the Bush camp hopes the seduction of Mark McKinnon is but a prelude to a national courtship built around Bush's warmhearted vision of conservatism.

"I was really impressed by his creativity, and I was particularly impressed by his honesty," Bush says by phone from Austin. "I'm a little skeptical at times of hired guns in politics. Some of them view the candidate as a product. But with Mark, we've run together, we've hiked at my ranch. I view him as a friend."

When he first met the Texas governor at a dinner two years ago, McKinnon says, "I went in with my guns loaded. I'd been drinking the Democratic Kool-Aid and had this notion that he'd just inherited everything and wasn't that sensitive. I met him and was instantly disarmed. I just liked him immediately."

Life is full of odd twists: McKinnon worked for Bush's Democratic predecessor, Ann Richards, and has turned down several offers to work for Bill Clinton. Yet he found himself the media adviser for Bush's 1998 reelection campaign, which the governor won in a landslide, and is now a key shaper of the message for the man who could well be Clinton's successor.

McKinnon, 44, has paid a price for his heresy. "Most of us think he woke up one morning with the dream many of us have of being welcomed in the Oval Office," says Peck Young, a Democratic operative in Austin who has worked with and against McKinnon in campaigns. "Mark realized there wasn't an opportunity to do that as a Democrat, so he switched. The man was making his grab for the brass ring. I don't think I would've made this particular grab."

Close friends have been more sympathetic. "Mark leads with his heart, and Bush won his heart," says Paul Begala, the former Clinton White House aide and fellow Texan. "He ain't a Republican. . . . I tease him that it's a midlife crisis, cheaper than a red convertible and more honorable than an affair."

Wary of navigating the Republican primary waters alone, McKinnon recruited Stuart Stevens, a veteran GOP adman who was the first in a series of media consultants for Bob Dole's 1996 campaign, to the Bunker, their bomb-shelter headquarters in Austin. They have more than a half-dozen spots edited and ready to go.

Both men speak of the value of positive advertising--a common refrain before the mudslinging season begins in earnest. They say they are ready to respond aggressively if Steve Forbes uses his personal fortune to bombard Bush with negative ads, yet without getting down and dirty. "We're not going to be Bambi in the woods," McKinnon says.

The Austin admaker favors a spare, unadorned style that consists mainly of having the candidate speak to the camera. "Being the media adviser for Governor Bush is kind of like being the jockey for Secretariat--you get in the saddle and let him run," says McKinnon, sounding like he's at least sipped the W. gang's Kool-Aid.

Still, McKinnon has been through enough difficult races to understand that his horse will not always be several lengths ahead of everyone else.

"There are always physics in politics, and in presidential races in particular, what goes up will come down. We'll have moments in this campaign where we're losing altitude. We can't go any higher than we are."

FANNING THE EMBERS

Mark McKinnon was suffering from advanced burnout.

"Maybe it was the candidate for statewide office who got so drunk he came on to a member of our film crew at a public restaurant while his wife and daughter sat horrified across the table. . . . Maybe I got tired of candidates' asking me what their firmly held convictions should be. . . . Maybe I got tired of being in a dingy campaign office a thousand miles from home missing yet another of my daughters' birthdays. Maybe politics just got old. Maybe I just got tired."

Whatever the reason--and he offered plenty like these, in a Texas Monthly piece he wrote in 1996--McKinnon had had enough. He started doing corporate work for his firm, Public Strategies, and left the political wars behind.

But then McKinnon--who tends to speak in well-rehearsed sound bites--met Bush at the fateful 1997 dinner and got a few invitations to the governor's mansion. "My political flame had been drowned, and he reignited the pilot light," he says.

The warming toward Bush came as McKinnon was reassessing a career in which he relentlessly bashed the GOP as heartless. "I could only see in black-and-white," he says. "I had to confess to myself that occasionally a Republican did something good, and there were bad Democrats. I hated the line-in-the-sand politics of 'we're always right, they're always wrong.' "

McKinnon understands all too well that he is part of the marketing pitch, the notion that open-minded Democrats may be drawn to Bush's centrist rhetoric of inclusion just as the media man was. Bush, for his part, seemed to value the fact that McKinnon wasn't from Washington, wasn't looking for the business and had to make a personal sacrifice--abandoning his party--to join the team.

McKinnon's old pals see him as misguided. "I trust Mark, I trust his judgment," says Democratic consultant Mandy Grunwald, a former colleague. But noting that Pat Robertson recently described Bush as more conservative than he appears, she says: "I have a hard time believing the same man can please both people and not be lying to one of them."

"Bush is a lightweight," says Begala. "He needs a guy like Mark who can give him the appearance of having a heart and maybe even of having a brain."

If McKinnon has broken the mold, it may be because he comes from anything but a cookie-cutter background. A doctor's son who grew up in Denver, he was befriended by singer Kristofferson, who heard his band, helped him make a demo tape and tried to get him a record contract. After his junior year in high school, McKinnon left home and hitchhiked to Nashville to hang with his hero.

"I wanted to be Bob Dylan, I wanted to be Jack Kerouac," he says. The only problem: "I was terribly untalented as a songwriter."

After finishing high school, McKinnon continued to pursue a music career, churning out songs and performing at whiskey joints. Eventually, though, he moved from Nashville to Austin, locked his guitar in a closet and enrolled at the University of Texas, where he wound up in an election for editor of the Daily Texan.

Upon discovering that one of his two rivals had engaged in resume inflation, McKinnon leaked the news to the other candidate, cruising to victory while they ripped each other apart. "It was my first political dirty trick," he admits.

McKinnon faced a personal crisis when, with American hostages in Tehran, police demanded that he turn over unpublished photos of an Iranian student demonstration. He refused and was jailed for a day. The case became a cause celebre, with students snapping up T-shirts featuring McKinnon's fingerprints. After graduation he married his high school sweetheart, Annie, and embarked on a new career.

Having covered Lloyd Doggett as a Texas legislator during his college days, McKinnon volunteered for the Democrat's 1984 Senate campaign, where he worked with James Carville and Begala, his college pal. Begala had McKinnon walk around with a sign festooned with rocks, to symbolize how David felled Goliath. Doggett won the primary only to get crushed by Phil Gramm that fall. McKinnon, who had been the campaign spokesman, was hooked.

But he had plenty to learn. While serving as spokesman for Texas's Democratic governor, Mark White, he faced a flood of questions about White's complicated financial disclosure reports. "It's not as bad as it looks," he said. During White's reelection campaign, McKinnon told an off-the-record gathering of journalists that his side was trying to portray Republican opponent Bill Clements as "a cold, heartless son of a bitch"--remarks that quickly got on the air.

McKinnon found himself in 1987 with two offers. One, from Clinton adviser Dick Morris, was to become the Arkansas governor's spokesman. The other was to join Buddy Roemer's long-shot gubernatorial campaign in Louisiana. McKinnon headed to New Orleans, and when Roemer won, his stock was on the rise.

"As a press secretary he was in a league with Mike McCurry," says Grunwald. "He had a great manner--relaxed, amiable, affable, but absolutely calculating. And unflappable. He did a lot of spinning, but nobody felt spun."

Karl Rove, a top Bush strategist who has worked against McKinnon, says McKinnon tried to recruit him to join Roemer's campaign when the Louisiana governor decided to seek reelection as a Republican. "He wanted to help his friend do the right thing, but he just couldn't bring himself to switch parties," Rove says.

McKinnon got an education in ad-making when he joined the New York firm of Sawyer Miller, where Grunwald worked. And, ironically, he toiled for Michael Dukakis's hapless presidential campaign against Bush's father.

He soon returned to Texas, signing on with Ann Richards in her successful 1990 bid for the Texas governorship. But his role was reduced after the primary. "Ann lost all confidence in him," a Texas operative says. "She didn't think he was tough enough." McKinnon won't discuss his falling out with Richards, but doesn't deny that he voted for her when she lost to Bush in 1994. He was, after all, a Democrat.

Begala, meanwhile, was trying to persuade his old pal to join the Clinton communications team. "I would have been seriously disappointed," McKinnon says with a tone of relief. "I look at how people treat their staff and friends. Bill Clinton has discarded people left and right like trash."

STOKING THE FIRE

Soon after the 1996 election, Bush says, McKinnon's Texas Monthly article on "how he'd gotten sick and tired of the politics of people tearing each other up caught my attention." And when they met, "I came away with the impression Mark actually thought I was a pretty good fella."

Karen Hughes, Bush's communications director, recalls the governor showing her a tape of McKinnon's ads. She says they liked the way he portrayed Bob Bullock, Texas's Democratic lieutenant governor, in "a very real fashion." Hughes was also struck by the way McKinnon put Houston Mayor Bob Lanier in a casual sweater.

By the time Bush asked him to handle his reelection campaign, McKinnon was smitten. "You could just see him falling in love," Rove says.

Still, McKinnon says, "it was probably the hardest decision I've ever made in my life." While he had grown more conservative since his Dukakis days, he had to grapple with "tough political questions I spent months agonizing over."

The spots that McKinnon made in 1998 provide both a preview of Bush's presidential campaign rhetoric and a glimpse of the advertising themes to come. There is black-and-white footage of head-shaved teenagers doing push-ups at a boot camp while Bush says that "discipline and love go hand in hand." He is seen hugging a black construction worker, a Hispanic woman, a disabled boy. He talks about "personal responsibility," whether the issue is boosting reading scores, discouraging teenage pregnancy or cracking down on welfare fraud.

Seated on a couch in a short-sleeve Western shirt and jeans as music swells in the background, Bush says: "For too long we've encouraged a culture that says, if it feels good do it, and blame somebody else if you've got a problem"--a line that's become part of his stump speech.

The governor was pleased with McKinnon's straight-ahead approach. "He was trusting me to be able to put out a message," Bush says. "He captured what I was trying to say to people."

But McKinnon also has a reputation for "throwing long," in political parlance--one that was cemented during Roemer's underdog Louisiana campaign, when the consultant suggested flying to Las Vegas and gambling the candidate's piddling $30,000 bankroll on a single bet. And then there was the "Terminator" ad, a lighthearted spot that put the reserved Texas Sen. Bob Krueger in a leather jacket and sunglasses. (He lost.)

Now, of course, McKinnon's candidate is a huge favorite who's raised a stunning $56 million. "The danger to a front-runner is being too careful and conventional," McKinnon concedes over lunch at a midtown grill. He is among the advisers who urged Bush to take the risk of criticizing the Republican Party for an uncaring image--as the candidate proceeds to do moments later in the Sheraton across the street.

The rail-thin McKinnon is clearly in physical shape for the marathon. He is a triathlete who once spent 13 1/2 hours competing in an ironman event: swimming 2.4 miles, biking 112 miles and running 26 miles.

Indeed, for a man who has pulled several all-nighters to finish commercials in recent weeks, he seems remarkably relaxed. He sometimes sneaks off in the afternoon to take a dip in a chilly limestone pool called Barton Springs, where he communes with the ducks and the turtles. Still, McKinnon knows that life in the Bunker could be the toughest competition yet.

"It's a bit like jumping out of an airplane and wondering if you'd packed your parachute," he says.

CAPTION: Longtime Democrat Mark McKinnon found himself looking at the Republicans in a new way. "I hated the line-in-the-sand politics of 'we're always right, they're always wrong,' " he says.

CAPTION: Mark McKinnon, lifelong Democrat and media adviser to George W. Bush, with his 8mm Honeywell camera.