Clad in a surgically attached polo shirt and jeans, Michael Moore takes to the streets of America, trying to figure out what the hell is wrong with this country. But is he a fearless leftist hero or just a manipulative bully with a camera?

Certainly, the guy has an occasional penchant for dangerous mischief, which is probably why some people are attracted to his films. At one point during Bowling for Columbine -- the prolific documentarian's latest opus -- Moore strolls into random Toronto homes to verify the assertion that Canadians leave their front doors unlocked at all hours of the day. It's a hilarious sequence, and the movie uses it to ask a terrific question: why is it that Canada -- a country whose love affair with firearms rivals ours -- has a gun homicide rate of just under 200 incidents a year, compared to our 11,000? Could it be, as a cornered Charlton Heston suggests late in the film, an "ethnic thing," or is the nightly fearmongering on the news to blame?

Moore has always made a point of asking more questions than he can answer. His wildly popular debut, 1989's award-winning Roger & Me, was the result of his tremendous outrage at the economic collapse of his hometown, Flint, Mich. The town was devastated when General Motors closed its local factory, leaving several thousand Flint residents jobless. Months later, Flint was named by Money Magazine as America's worst place to live.

The movie, which would go on to become the highest-grossing documentary of all time, intercuts footage of Moore's quest to confront General Motors CEO Roger Smith with a profile of the town after the plant's closing. Through his quixotic, ultimately futile battle, Moore bravely tries to penetrate Smith's cavalry of defenses -- security guards, secretaries, spokespeople, shareholders, health club managers, pesky key-activated elevators -- in an effort to convince the General Motors' honcho to return to Flint and confront the havoc his company has wreaked.

The documentary epitomizes Moore's entertainingly relentless approach. Wise to the fact that hounding a symbol of corporate greed was what made Roger & Me a critical box-office smash, Moore spent much of his subsequent career continuing that tradition. In 1997's The Big One, his second theatrical documentary, (it was preceded by a fictional offering called Canadian Bacon, and the television series TV Nation), he travels to 47 cities on a book tour, promoting the recently published Downsize This!: Random Threats from an Unarmed American. In each of his destinations, he visits a corporation, performing stunts like presenting human resources personnel with a "Downsizer of the Year" award and giving others an 80-cent donation to cover the cost of the first day of labor by one of their newly hired Mexican workers.

This is all very funny, and fun to watch, but it doesn't serve Moore well in intellectual circles. Though he has repeatedly claimed that he is an entertainer first and a political activist second, the lofty goals of his documentaries call his objectivity into question. He is certainly good at making generally innocent PR flacks come off as Grade A assholes. But it's their job to get rid of inquiring minds like himself, and his provocations threaten the accuracy of his depictions.

The culmination of Bowling for Columbine occurs when National Rifle Association chief Charlton Heston permits Moore to enter his home for a one-on-one interview. Moore proceeds to attack the Ten Commandments star -- who, in a piece of bad timing for Moore, reveals that he is battling Alzheimer's -- with unanswerable questions, forcing him to first spout the aforementioned "ethnic" epithet, and then to unceremoniously kick the filmmaker out. This sets up the film's emotional climax, in which Moore chases Heston with a photo of a school shooting victim.

Such ambush tactics certainly call Moore's validity as a reliable information source into question. But there's little doubt that he is passionate, sincere, endearingly tenacious and has a wicked sense of humor. His films work not because they are detached analyses but because it seems that he has poured his heart and soul into their making.

Columbine is a polarizing work that is essential viewing for anyone with even a cursory interest in the roots of America's obsession with violence. Moore neither presumes to know what those roots are, nor does he claim to have a solution. His mission is not to preach, but to provoke us, to make us angry, sad and curious.

After barging unannounced through a befuddled Toronto resident's unlocked door, Moore retreats with a sheepish "Thank you for not shooting me." Hero or bully, he is certainly fearless.