One of John McCain's oft-cited attributes is his humor. He says it fortified him as a POW in Vietnam, and who are we to argue with that? It's endeared him to a press corps that can't seem to get enough of his straight talk, especially when it's deep-fried in corniness. The ability to laugh has also blunted the edges of some of McCain's more provocative moments on the stump: The "Bomb Iran" ditty he sang to the tune of the Beach Boys' "Barbara Ann" was disturbing, sure. But on the continuum of crazy right-wing uncle behavior, it was more like not knowing when to stop complimenting little Sally on what a finely turned out and healthy young lady she's become, not like shooting the family dog, which Cheney would do before turning the rifle onto the bipeds. McCain's demonstrated a winning way with self-mockery ("Time was I could knock up Cleopatra just by winking at her") and the kind of venom-less satire that's made him the most frequent guest and foil on the Daily Show, as well as the most at-ease pol performer on SNL (remember Steve Forbes as a construction worker?). As against Hillary's robotic attempts at mirth, which only Diane Ladd in a David Lynch film could adequately capture, and Obama's intellectual suavity, which belies his inner law geek, McCain is the knuckle sandwich-giver of this election. And while it's true that voters esteem personality above policy, his humor could well be more of a liability than an asset.

1. The mirth of the gallows doesn't work on the hustings. McCain once tried to deflect Jon Stewart's criticism of his oh-so-cavalier and flak-jacketed tour through the Baghdad marketplace by saying, "I had something picked out for you, too - a little IED to put on your desk." Not quite a knee-slapper (let's not call it a "dud," shall we?), it was nonetheless a line that wouldn't have been out of place in a barracks or a foxhole, where one way to cope with death is to laugh at it. But such flippancy was definitely not ready for prime time, even a basic cable comedy show. McCain only seemed to underscore a reckless disregard for the consequences of the Iraq war, which is why Rep. John Murtha landed a solid blow in a House floor speech: "In the last four months, we've lost more troops than any other period during this war. Imagine a presidential candidate making a joke about IEDs when our kids are getting blown up! It's outrageous!" McCain was only spared a greater round of censure by his own hard-earned epaulettes, and yet he didn't help convert any wincing liberals to his side when he responded by telling his fellow veteran to "lighten up" and "get a life." If he does something like that now that's he's the nominee, he won't survive it as easily. Far less will he if he's president.

2. He's not the Gipper. The first association America made with Ronald Reagan was as a dapper Yankee Doodle whose greatest co-star was a chimp and second greatest was a wife he'd never even dream of calling a "cunt." (Kiss your mommy with that mouth?) Also, he ran right after what had to have been the most humorless presidency in U.S. history (the comedy on Jimmy Carter's part was unintentional, anyway), and up against the glowering commissar severity of our ideological enemy, a doddering Falstaff seemed tonic. When Reagan told Soviet jokes about waiting ten years to get a car, they worked not only because pessimistic Russians had invented them, but because Western anti-Communists – Republicans and Democrats alike – knew that the core messages rang true. His communication style was folksy and plain, but it unified the country in a way that has evidently impressed Barack Obama and led to some not-so-counterintuitive comparisons between the two candidates (one thinks his great uncle liberated the wrong Nazi death camp, the other thought seeing it done on screen meant he'd done it in reality).

Even Reagan's biggest Armageddon-flirtatious gaffe – "We begin bombing in five minutes" – was intended for a private audience of NPR technicians, who found it amusing at the time. And after what popular science fiction franchise could McCain ever hope to name a defense system in the age of sacred terror?

Reagan would never have made a "gaydar" joke, as McCain did on his recent SNL appearance (this came in the middle of a prolonged riff about his antiquity, which his handlers had better realize soon is better ignored than lampooned). The shtick might play in the blue and purple states, chock full of socially liberal Independents and cross-over Democrats as they are, but it won't play in Peoria. Nor will it help McCain with evangelicals and other movement conservatives, who as might as well be teased with, "Didja hear the one about Pilate trying to wash his hands hopped up on OxyContin?"

Reagan, too, was old when he decided to run, but his shoe polish dye job and only marginally saggy good looks (also compare to Carter) helped convince everyone he was young enough to freestyle summit with Gorbachev. Most important, the senility rumors took hold after he got elected.

3. We've had 8 years of a comedian-in-chief. Clearly the most damaging point is that McCain's wisecracking will only remind people of the smirking jester in the White House now. A few months back, New York magazine recounted a set piece from Faith of My Fathers, the GOP nominee's memoir, about his hard-drinking, hard-womanizing days:

Once, while journeying to meet his girlfriend's parents at their home for the first time, McCain had a short layover at a Philadelphia train station. He sat down at the bar, in his uniform, and caught the eye of "several friendly, inebriated commuters" who bought him enough drinks to make him miss his first three trains. When he finally arrived at his girlfriend's house, plastered and hours late, he walked up the front steps and fell through the screen door. The girl's father thanked him for coming and called him a cab. McCain never saw the girl again.

Disarming though this may be to tell at the cigar bar or on the racketball court, it comes perilously close to the content of Oliver Stone's W., which will remind theatergoers of another rehabilitated party-boy with ambition.