An essentially dignified and thoughtful performance by Sen. John Kerry, contrasted with an oddly giggly turn by President Bush, combined to give the last debate of the presidential campaign to the challenger last night, but very narrowly.

Bush seems to have been taken apart and put back together again after each debate, reassembled according to estimates of how he'd done. Last night it looked as though his handlers had told him to smile, smile, smile, especially when Kerry was trying to make points, points, points.

The debate, televised on all the networks from Arizona State University in Tempe and expertly moderated by CBS News correspondent Bob Schieffer, was supposed to concentrate on domestic issues. But Schieffer's very first question -- would Americans ever feel truly safe and secure again? -- gave Kerry the immediate opportunity to trot out his much-vented criticisms of Bush's Iraq war and gave Bush a chance to crow about progress in Afghanistan.

Kerry charged that Bush had once said terrorist mastermind Osama bin Laden was not someone he worried about, and Bush denied ever having said such a thing. But during otherwise adamantly pro-Bush analysis on Fox News Channel after the debate, the commentators had to agree that the record showed Bush made such a statement not just once but twice.

Bush's reaction to Kerry's charge, like several of his statements and facial expressions throughout the 90 minutes, was eccentric. "That's kind of one of those 'exaggerations,' " he said, emphasizing the word and grinning as if he'd just made the wittiest quip of the year. Then again, near the debate's end, Kerry referred to what he considered the two greatest commandments as "the two greatest amendments," kind of a natural gaffe for a longtime legislator.

Kerry wore a long puss through most of the evening, but Bush looked as smiley as Clarabell the Clown. Kerry did show a sense of humor when answering Schieffer's last question, about what it was like to be surrounded by "strong women," including their wives and daughters. Kerry said all three men, including Schieffer, were "lucky people who married up, and some would say maybe me more than others," a reference to his inordinately wealthy wife. The crowd gave him a warm laugh and seemed relieved to see that Kerry can laugh at himself.

ABC's Peter Jennings said just before the event, "If there's ever been a more important debate, it certainly doesn't come to mind," which may have been something of an exaggeration, but there was a palpable tension in the air, since this last debate was likely to linger in voters' minds. The cable news networks had the luxury of time to spend on pre-debate warmups, but some dimwitted producer at CNN stationed Wolf Blitzer and his co-anchors in front of a shouting, chanting crowd of students, roaring so loudly they all but drowned out whatever Blitzer and colleagues were saying.

Blitzer did manage to make himself heard when delivering a CNN promo, however, promising that the network's coverage would be "unprecedented" and imploring viewers to "please be sure to stay with us for the rest of the campaign." Anchors should not have to be salesmen.

Schieffer's questions were thoughtful, comprehensive and well worded, though there was no practical way to keep the candidates from repeating their favorite buzzwords and slogans as often as they could. Bush must have said 98 times during the debate -- or so it seemed -- that Kerry had voted 98 times to raise taxes. Kerry didn't go long before saying "I have a plan," in this case a plan for health care during the upcoming flu season. He also mentioned at every opportunity -- or else created an opportunity to mention -- that Bush's tax cuts allegedly benefit only the richest Americans.

Good Lord, if I hear that one more time I will shriek.

Bush blamed the shortage of flu vaccine on lawyers, one of his favorite targets, but appeared to contradict himself. He said manufacturers were afraid to produce the vaccine for fear of getting sued, yet he also said that some of this year's supply of vaccine was "contaminated" and could not be used.

Kerry said he advocated a "pay-as-you-go" plan for the national budget, which Bush shortened to a "pay-go" plan, sneaking in an irrelevant reference to Sen. Ted Kennedy, with whom Bush and Vice President Cheney are always trying to link Kerry. When Schieffer asked a question about jobs, Bush took his cheapest shot of the evening, ignoring the question to say to Kerry, "There's a mainstream in American politics, and you sit right on the far left bank," then adding that Kerry was so liberal he made Kennedy look like the conservative senator from Massachusetts.

It was crummy behavior for a president of the United States, the kind of thing better left to lap-dog pit bulls such as vice presidents.

Schieffer asked about homosexuality. Bush said he didn't know if homosexuality was a choice or something predetermined before birth, though if he had bothered to read the latest studies he would know that current scientific thought favors the latter. "I believe in the sanctity of marriage," Bush said, defining marriage as a union between a man and a woman. Kerry basically concurred and managed to mention that Cheney has a lesbian daughter, which may have been a cheap shot of his own.

On the subject of abortion, Bush charged once again that his opponent was "out of the mainstream." When the subject turned to health care, Kerry said, predictably, "I've got a better plan." Schieffer had quoted news media in framing the question and Bush, grinning, said, "In all due respect, I'm not so sure it's credible to quote leading news organizations about -- never mind." Then he laughed robustly at whatever joke he was telling himself.

As at the previous debate, Bush came charging out of the chute last night, on the defense or the attack with equal vigor, yet usually maintaining a Cheshire-cat grin that seemed to imply he did not take Kerry seriously as a challenger and wanted the national viewing audience to know that. Questions he found hard to answer, he just ignored. Kerry argued that the minimum wage should be raised when Schieffer asked about that, but Bush simply launched into a soliloquy about education.

There was talk of Roe v. Wade, gun control, faith-based decision-making and the way America has become polarized under Bush. Kerry's closing statement was eloquent; Bush's was less so. As in the first debate, Kerry behaved presidentially while Bush came across as much less imposing and serious.

"A spirited and wide-ranging debate" was Tom Brokaw's estimation on NBC. Jeff Greenfield on CNN, talking over the roar of those rackety students again, felt that "neither candidate" made the most of his opportunity. Over on Fox, though, everybody threw bouquets at Bush, especially that sickening, simpering suck-up Morton Kondracke, who hailed a "much better performance" by the president than last time. Smirking right-winger William Kristol said that of Bush vs. Kerry, "He slaughtered him," a manifestly ridiculous contention.

Nobody slaughtered anybody. The real mystery is how many American minds found either candidate persuasive enough to lock in a vote based on that debate, or even on all three presidential debates (plus one vice presidential debate) put together. The political year is clearly improved by the presence of the debates, however awkward and clunky the formats sometimes are, but the candidates doing the debating still tend to be motivated more by the fear of making a mistake than by the courage of whatever convictions they actually have.

Nobody won big last night, including the American people.

In their final debate, Sen. John Kerry and President Bush again brought out their well-worn buzzwords and slogans.A point by President Bush draws a grin from Sen. John Kerry during their debate in Tempe, Ariz.