George Bush has a secret weapon in his re-election bid

If the title Stupid White Men doesn't mean anything to you, then you can't have been anywhere near a bookshop in 2003. Either that, or you are so used to picking your way through the piles of Michael Moore books that you no longer notice them, or the accompanying recommendation: "Staff pick! Really cool - the book that exposes Dubya as a fascist."

Moore is the American slob in a baseball cap who likes to hint - only hint, mind - that President George Bush had a hand in the September 11 attacks. He has a huge following on campuses on both sides of the Atlantic: he, more than anyone else, has persuaded British students that the current occupant of the White House is, like, just such a moron.

Stupid White Men was the bestselling non-fiction hardback in Britain last year, after the Atkins New Diet Revolution; it's now top of the paperback list. Bowling for Columbine, the feature-length documentary in which Moore blames a high school massacre on the Republicans, won an Oscar.

Moore's new book, Dude, Where's My Country?, offers his most sophisticated critique to date of American foreign policy: "We like dictators! They help us get what we want and they do a great job of keeping their nations subservient to our galloping global corporate interests."

It takes Moore just a couple of paragraphs to absolve Osama bin Laden of the destruction of the World Trade Centre. "How could a guy sitting in a cave in Afghanistan have plotted so perfectly the hijacking of four planes and then guaranteed that three of them would end up precisely on their targets?" he asks.

Viewers of Bowling for Columbine may find this puzzling, remembering the film's insistence that "Osama bin Laden used his expert CIA training to murder 3000 people"; but Moore regards consistency as the hobgoblin of little minds.

And, besides, his fast-morphing conspiracy theories are all built on the same, unshakeable foundation. Everything in the world is the fault of stupid, white Americans - in which category he apparently includes the September 11 plane passengers: he has a stand-up routine in which he suggests that if the victims had been black, rather than white "scaredy-cats", they would have had no trouble overpowering the hijackers.

The American right used to dismiss Moore's material as unfunny agitprop, unworthy of attention. That is not quite fair. Bowling for Columbine is a brilliantly constructed documentary; it's hard not to cheer when Moore embarrasses the Kmart chain into banning the sale of live ammunition to teenagers. The books are dismal by comparison, but even they evince the odd chuckle.

With sales of Stupid White Men creeping up towards 4 million, the right has changed tactics. Its new approach is to denounce Moore as a liar - a more promising line of attack. And it is certainly true that Bowling for Columbine turns out to contain more half-truths than an Enron corporate video.

For example, Moore says that Lockheed Martin manufactures "weapons of mass destruction" in Littleton, Colorado, the town where the Columbine killings occurred; he even grills a company executive in front of a scary-looking rocket in the local factory. In fact, Lockheed Martin doesn't make weapons in Littleton; it makes weather and communications satellites that are launched by rocket.

Then there's the scene in which Moore opens an account in a rural bank and is given the free shotgun offered to new customers. "Don't you think it's a little dangerous handing out guns in a bank?" he asks. It's a good question. And the answer is: the bank doesn't normally do anything of the sort. Customers have to wait six weeks for background checks. According to the bank, the scene was staged at Moore's request.

Even the documentary's title is dodgy. It's based on reports that the Columbine killers went bowling on the morning of the massacre. Police investigators later concluded that the reports were untrue. The film makes no mention of this.

So generous is Moore's notion of artistic licence that the internet is now crawling with websites exposing his "lies". Some of his critics have gone further, and attempted to turn his own methods on himself. A documentary maker called Michael Wilson has been following him around, badgering him for an interview - just as Moore used to do to bloated chief executives. But Moore isn't talking. (Here's a tip for Wilson: if you want to catch up with Moore's entourage on one of his British visits, check out the Ritz.)

Meanwhile, Dude, Where's My Country? is sitting happily in the bestseller lists. Moore's fans don't care how many fast ones he pulls because, hey, he's a funny guy. There is nothing the right can do to dent his popularity. And perhaps it shouldn't even try.

The truth is that George Bush owes Moore a debt of gratitude. He wouldn't be president if it weren't for Green candidate Ralph Nader, who vacuumed up votes that would otherwise have gone to Al Gore.

Moore was Nader's biggest celebrity backer. So we can be reasonably sure that at least 538 Florida students voted Green because Mike told them to, thereby handing Dubya his winning margin.

And next time? Strange though it might seem, Moore could help the President achieve a second term. There he stands, inciting his audience to ever greater heights of Bush-hatred. The snag is that, although this goes down a treat in cappuccino-sipping Berkeley, it doesn't play so well among blue-collar voters who think Saddam deserved to get his backside kicked.

Histrionic invective directed against relatively popular sitting presidents rarely pays off, as the McGovernites discovered in 1972 and the Clinton-haters did in 1996. The sheer incontinence of the attacks on Bush by Moore and his Hollywood friends could help deliver the Midwest to Bush.

And Bush knows it, too. There's a curious passage in Stupid White Men in which Moore confesses that, on the rare occasions he has met George or Jeb Bush, they have teased him in an almost affectionate fashion.

Indeed, the more vigorously Moore attacks the President, the better Bush's approval ratings. Funny, that. And Moore's lifestyle has been awfully lavish of late. One doesn't want to sound like a conspiracy theorist, but it makes you think, doesn't it?