In a few months, if things go to plan, he will lob the product of some of that money into the already bloody American electoral battlefield with the release of his upcoming film Fahrenheit 9/11. The film examines the relationship between the Bush and Saudi dynasties, and offers a critical view of the experiences of soldiers and their families in the Iraq war. On Saturday it won the coveted Palme d'Or at Cannes. And, during a tight presidential race in an increasingly polarised nation, some are now asking whether the film could play a role in losing Bush the election.

At this stage, there remains the possibility that things will not go to plan. Earlier this month Disney blocked distribution of the film, claiming it risked politically alienating too many people. The question of who gets to see Fahrenheit 9/11, and where, will determine whether it affects the outcome of the election. Drawing big crowds in Democratic heartlands such as Los Angeles or New York will make little difference. If the film reaches the malls of Ohio, New Hampshire, Iowa and Missouri, however, it will be a different matter. "Moore has got to get it into the cineplexes and multiplexes," says Steven Schier, professor of political science at Carleton College in Minnesota, "and now that he has won at Cannes the force of the market could possibly push it there."

Presuming Fahrenheit 9/11 does find a distributor, its release will be a political event. According to the Washington Post, Miramax Films has hired a team of hardened Democratic apparatchiks - including Hillary Clinton's former campaign presssecretary, Howard Wolfson, top Gore adviser Michael Feldman and Clinton White House advisers Mark Fabiani and Chris Lehane - to help counter any Republican attacks on the film.

So will it have any effect? "My guess is that all the people who will flock to see it were not going to vote for George Bush anyway - in other words, he is preaching to the converted," says Howard Kurtz, the Washington Post's media correspondent.

New York Times columnist Frank Rich would have agreed before he became one of the few people to have seen the film. "Ordinarily, I'd say it would have no effect on the election," he says. "There are two factors that could change that. First, the film itself - its second half has an emotional punch that may bring in less ideological audiences, should word of mouth take off. Secondly, the amount of publicity attending the movie, starting with the fight (contrived or not) with Disney. That may turn it into a commercial phenomenon that reaches across party lines to a larger audience than the niche reached by, say, Bowling for Columbine [Moore's last, Oscar-winning film]."

But if Moore is a divisive figure, he is speaking to an increasingly divided country. Polls show a nation deeply polarised on partisan lines, where the key factor in the forthcoming election will be not how many people you can get to switch sides but how many of your own side you can get to turn up at the polls.

"He will clearly be speaking to one side of the aisle," says Vanity Fair columnist Michael Wolff. "But for the Democrats, this election is not going to be about how much you love John Kerry, but how much you hate Bush. And Michael Moore is one of the prime exponents of that crucial emotional underpinning to Bush hatred."

With polls showing the main candidates so close, Moore's film is likely to have the greatest effect on both the rightwing and leftwing edges of the Democratic base, rather than the huge swathes of "yellow dog" Democrats - so called because they would vote for the party even if it stood a yellow dog for office. On the left are those who might back the independent, anti-war candidate Ralph Nader. Moore backed Nader in 2000, when the latter was widely criticised by Democrats for handing the election to Bush. A recent poll suggests Nader's running could be decisive, with Bush at 46%, Kerry at 43% and Nader at 7%. Separate polling shows that in at least half a dozen swing states Kerry would beat Bush in a two-horse race, but lose if Nader were standing. This time Moore has urged Nader not to run and is backing Kerry.

"It could make a difference with Nader voters, given Moore's history with Nader," says Todd Gitlin, professor of journalism and sociology at Columbia University in New York. "Insofar as the film suggests that people must find a way to do everything they can to defeat Bush."

Among more mainstream voters, the effect could be more subtle. "To say it won't win over people who might vote for Bush may be too mechanical a view of the way that public opinion works," says Jeremy Pikser, screenwriter of the political comedy Bulworth. "I can imagine that it could strengthen opinions on how completely rotten Bush is among people who didn't hate him before, and then they might have a conversation with someone at the water cooler who is not completely wedded to Bush and win them over."

Just as hatred of Bush can mobilise Democrats, so loathing of Moore may motivate Republicans. Moore-bashing has become something of a cottage industry, with websites such as Moorewatch.com - who "watch Michael Moore's every move" - posting regular diatribes against the film-maker. At times, the criticisms get personal. Speaking of Europeans' love for Moore, Christopher Hitchens said last week: "They think Americans are fat, vulgar, greedy, stupid, ambitious and ignorant and so on. And they've taken as their own, as their representative American, someone who actually embodies all of those qualities."

On CNN last week, rightwing pundit Tucker Carlson said: "Michael Moore alleges the following things: that President Bush is responsible for the terrorist attacks of September 11; that Bush's family is connected to Osama bin Laden in some important, sinister way; and that Bush intentionally caused the deaths of thousands of people in the war with Iraq simply to enrich his friends in the oil industry." Referring to the former Clinton and Gore advisers on the Miramax team, he asked: "What happens when the lunatic fringe and the mainstream of the Democratic party become indistinguishable?"

It was not clear whether Tucker had seen the film or not, but Pikser points out that Republicans don't have to have seen it in order to misrepresent it. "They're very good at that. Just as many liberals didn't see the need to actually watch Mel Gibson's The Passion in order to know that it was anti-semitic, so Republicans don't need to see Moore's film to hate it, or him, and use it accordingly."

For the time being, conservatives' attentions are elsewhere - focusing on the calamitous situation in Iraq and Bush's equally calamitous plunge in the polls. Several were asked to comment for this article, but none responded. But for liberals, Moore's forthcoming film is one more reason to imagine what, until a few months ago, they thought was unimaginable - that Bush could lose.

Katha Pollitt, a liberal columnist for the Nation, said: "I haven't seen it, but it sounds like a 100-minute negative ad against Bush and co. And negative ads work."