You've had it drummed into your skull since junior high civics class: Every single vote counts. Diebold machines and hanging chads notwithstanding, it's still a resonant, if improbable, message: Any citizen of our nation might cast the deciding vote in an election. "Swing Vote" puts a seriocomic twist on the premise, turning a trailer park layabout (Kevin Costner) into the sole decider of a presidential tie.

Through an electoral college stalemate, the race comes down to the swing state of New Mexico. It comes down, in fact, to Bud Johnson, a beer-marinated single dad who promised his socially responsible 12-year-old daughter (Madeline Carroll) that he would shake off his usual lethargy and visit the polling station. Through a mechanical malfunction, Bud's ballot is not recorded, and he's allowed to cast it again. But first he's courted one-on-one by the Republican incumbent (Kelsey Grammer) and Democratic challenger (Dennis Hopper) who converge on his flyspeck home town to convince disenfranchised Bud that they deserve his vote.

The film's strengths are Costner's laid-back work as Bud, an affable ignoramus with a heart of gold, and the absurd policy contortions the candidates go through to woo him. In a series of satirical campaign commercials, the conservative beams approvingly at gay couples and champions environmental protection while the liberal lashes out at Roe v. Wade and praises "God's intelligent design." The bits are funny in and of themselves. The antiabortion spot features a playground full of happy children who vanish one by one in little mushroom-cloud poofs. But the ads are also a well-deserved poke at candidates' tendency to wuss out, compromise their ideals and run to the middle as Election Day nears.

Costner is a past master at this kind of lovable loser role. He's blissfully silly in a scene where he hears a no-nonsense knock on the door, concludes that the child protection authorities are after him again, and slips a crucifix necklace over his daughter's head. Hopper successfully plays against type as the milquetoast Democrat and Grammer brings some executive gravitas to the part of the president.

To give the story a touch of vérité, a slew of media personalities join the journalistic invasion force that descends on Bud's single-wide. Chris Matthews, Aaron Brown, Larry King, Arianna Huffington and Bill Maher play themselves. The film is handsomely produced -- Costner poured $21 million of his own money into it -- with an all-star cast including Stanley Tucci and Nathan Lane as PR spinmeisters. Like many vanity projects, it's a bit overlong and self-important.

Still, its heart is in the right place. At a time when 80 percent of the public despises political officeholders, it's fun to see them take a shellacking. Yet "Swing Vote" doesn't take the facile route of mocking and blaming politicians, with Costner's character as national savior. Bud has convictions, sort of, and a core of decency, but he's woefully underinformed and lazy -- a real mainstream American, the film implies. His precocious daughter shames him into making more of an effort to understand the issues and the consequences of his decision.

"Swing Vote" captures the spirit of an election year when many once-apathetic Americans are keenly interested in the outcome. We have met the enemy and he is us. But so is the hero.

Colin Covert • 612-673-7186