Any American citizen who feels betrayed by his government can vote differently next time, or write his local representative. But “Shooter,” a ham-handed conspiracy picture directed by Antoine Fuqua, proffers the notion that if that citizen is an ex-marine sniper with a knack for explosives, his range of options is a lot more exciting.

“Shooter” is an abnormally outspoken example of its genre, but otherwise it’s an old-fashioned action movie. That is to say, it’s really dumb. Remember a few years ago, when Matt Damon’s brisk “Bourne” thrillers made the viewer play catch-up? They managed to convey that certain CIA higher-ups had gone rotten without having them bellow it into the camera. They acknowledged that some of us who like to watch gunfights and car chases do in fact have brains. The Bourne pictures may even have gotten some people saying that a new batch of sophisticated action flicks was on the way. At times, “Shooter” seems to have been made specifically to shut those people up.

Bob Lee Swagger (Mark Wahlberg) lives as an enemy of the state might — in a cabin, with his dog and his rifles — but in fact he has the stuff heroes are made of. Three years ago, this gunnery sergeant watched his best friend die after their commanders abandoned them on a top-secret mission in Ethiopia. “This is a man with a history of duty and patriotism,” says a former colonel (Danny Glover) who wants to track Bob down and put his sniping skills to good use.

Make that bad use. The colonel comes from the Beltway’s shadier corridors, and it turns out he’s not being entirely truthful when he tells Bob he needs his help foiling an assassination plot on the president. The colonel’s boss, a U.S. senator (Ned Beatty), wants to cover up a vicious oil grab in Africa and Bob, though he doesn’t know it, is going to help.

Things go bang all at once, making Bob — played athletically but somewhat indifferently by Mr. Wahlberg — the target of a nationwide manhunt. His only allies against the F.B.I. and the colonel’s network of ex-military goons are his late partner’s widow (Kate Mara) and a rookie F.B.I. agent (Michael Peña), although the building-supplies store that sells him enough raw material for a one-man assault on a heavily guarded enemy base surely deserves special thanks.

Admittedly, the film’s “MacGyver”-like showcase of emergency improvisation — Bob always knows how to make a fusebox or a gas pipe work for him — is hard to resist. What’s not to like about a hero who can hot-wire a car, build his own remote-controlled explosives, and turn sugar and bottled water into a makeshift IV? Moments before he has some bullets removed, Bob puts himself under by huffing a can of whipped cream. (In the production notes, the marine who helped Mr. Wahlberg train for the role says he hopes audiences will leave the film with a “more accurate” understanding of what scout snipers do. I’m not sure this is what he had in mind.)

Of course, Bob’s coolest skill is the one that allows him to blow a guy’s thumb off from half a mile away, which he demonstrates during the film’s best set piece, a shootout set in a high-altitude snowfield. The victim, a sadistic heavy who has tortured the dishy Ms. Mara, starts cackling with delight: He can’t believe Bob took the shot. Then Bob takes another. He isn’t laughing so much after that one.

A round of unconventional warfare on a wintry expanse also provided the highlight of “King Arthur,” Mr. Fuqua’s unexceptional previous feature. Both films suffer from the same battering-ram insistence on the theme of endangered democracy — first in the aging Roman empire, now on the homefront. Fortunately, as these films remind us, we have movie stars like Clive Owen and Mr. Wahlberg to prevent — or at least delay — the republic’s decline and fall, or, as Mr. Beatty’s porcine senator puts it, “one confused soul who thinks one man can make a difference.” Unfortunately, these films also feel the need to stop and explain what they’re fighting for every two seconds.

In this case, even that part doesn’t add up. “Shooter” is a payback fantasy that targets cynicism and selling out in Washington. That’s awfully rich, considering the early scene in which the hero’s dog opens the fridge and fetches him what is clearly a Budweiser. And what to make of a movie that purports to condemn torture (“We know the bosses knew” about Abu Ghraib, the senator adds for good measure) but provides, for our viewing pleasure, the image of a barely clad Ms. Mara about to receive it? If “Shooter” can’t stick to its guns, it should, well, just stick to guns.