You’d think comedians would want to be remembered for their wit rather than the sound of their own laughter. Unfortunately, the treadmarks left on your eardrums by the new documentary, “Al Franken: God Spoke,” come from Mr. Franken’s incessant cackling at his own jokes. He opens his mouth, says something, and out comes a gratingly guttural “hah hah hah.”

There’s no variety or gradation to the laughter. No matter the circumstance, it sounds exactly the same, as if all humor were created equal. It’s an odd position in which to find oneself: to be a comedian with a horrible laugh. Slightly chubby, with tousled locks, big teeth, and horn-rimmed glasses, the 55-year-old “Saturday Night Live” alumnus is a mostly genial presence, but appears to be utterly unaware of his affliction.

Produced by D.A. Pennebaker and directed by Nick Doob and Chris Hegedus — the team behind “The War Room,” the hit documentary about Bill Clinton’s 1992 election campaign — “Al Franken: God Spoke,” is slick cinéma vérité that tracks Mr. Franken as he travels the land stumping for John Kerry during the 2004 election campaign. It was a time when MoveOn.org started flexing its Internet muscle, Mr. Franken’s book “Lies and the Lying Liars Who Tell Them: A Fair and Balanced Look at the Right” topped the New York Times best-seller list, and Michael Moore’s “Farenheit 9/11” was burning up multiplexes across the country. Heady days for the Left, as anyone who attended a “Take Back America” convention or spent five minutes at a MoveOn “house party” mixing cocktails with conspiracies can tell you.

The film’s chief conceit is that while Republicans are dough-brained dittoheads who endlessly repeat the party line, Mr. Franken and his cohorts are deep and nuanced thinkers. So one wonders why the film treats the famously nuanced Senator Kerry, for whom Mr. Franken worked tirelessly, like a mad windsurfer best kept hidden in the attic. Until we hear a few words from his concession speech near the end of the film, he’s basically invisible. Could it be that, like many ardent Democrats, Mr. Franken secretly despised the candidate he so desperately urged his countrymen to vote for? If so, he isn’t telling.

A key scene comes early on, when Mr. Franken defines his brand of political comedy before a group of wide-eyed, reverential students. “What I do isn’t propaganda,” he tells them.”What I do is taking what [Republicans] say and using it against them. It is ju-jitsu. They say something ridiculous, and I subject them to scorn and ridicule. That’s my job.”

The fact that he’s often good at his job is what makes this smoothly directed documentary palatable and sometimes entertaining. He tells some funny jokes, and is particularly adept at impressions of politicians — something we can all enjoy. He does an excellent Dick Cheney, and at an upscale Republican cocktail party, talks in a deep, rumblingly Kissinger-esque voice, vocal chords seemingly lodged in his abdomen, to none other than Mr. Kissinger himself. (The behavior is boorish but the imitation is good.) Best by far is his send-up of the late Strom Thurmond, which is truly funny because it transcends politics and gets at something elemental about race, sex, and male desire.

Still, Mr. Franken’s satire rarely rises above the level of crudely barbed insult as he baits the likes of Bill O’Reilly and Ann Coulter.The title of one of his bestselling books,”Rush Limbaugh Is a Big Fat Idiot,” gives you the general idea.

Americans who dislike the current administration may find much to admire in this film. As if to assure us of Mr. Franken’s virtue, we are repeatedly informed about the duration of his marriage (28 years) and shown footage from one of his four USO tours, in which he entertains the troops in Iraq. We see the beginnings of Air America, the liberal radio station Mr. Franken helped launch in 2004, and follow him to the Republican National Convention in New York, where he goes mano-a-mano with conservatives Sean Hannity and Michael Medved and is predictably shown landing the hardest blows.

After Mr. Kerry’s electoral downfall, we also witness the first stirrings of Mr. Franken’s desire to contest the 2008 Senate seat in Minnesota, the state in which he grew up and to which he has returned in preparation for a possible run. (He was born in New York.) Although it is not yet certain whether he will become a candidate, in many ways he seems ideally suited to the job. He’s as thick-skinned as a reptile, he’s a born back-slapper (gender-neutral to a fault, he claps women on the back as if they were football players), and he is enchanted by the sound of his own voice. Indeed, one could be forgiven for considering this independently made but nakedly promotional film the first draft of a campaign commercial. By the dismal standard of the genre, it has to be called first rate.

It’s tempting to criticize Messrs. Doob and Hegedus for not giving viewers a deeper sense of what makes their subject tick, or to what probing the extent to which Mr. Franken’s idealism is interwoven with a hidden lust for power. But to advance such a critique would be to misunderstand the filmmakers’ subject. Just as our current president is frequently flailed by Democrats for his apparent lack of introspection, it turns out that one of his biggest critics is equally extroverted, if not more so. What you see, and hear — “hah hah hah” — is pretty much what you get.