Everything good about "Our Brand is Crisis" is contained in the opening moments, in which Sandra Bullock, playing a political consultant, is interviewed as if for a documentary. She talks about how she used to admire politicians before she started working for them, and there’s something about her combination of ironic humor and deep-baked disillusionment that suggests a world of ugly experience. To see her is to want to take the movie’s journey and learn what she knows.

"Our Brand is Crisis" has unusual origins. It’s a fictional feature, but it’s based on Rachel Boynton’s documentary of the same name, about the impact of James Carville’s political consulting team on a Bolivian presidential election. This fictional reworking pits two American consulting teams against each other — one led by Bullock and the other by Carville look-alike Billy Bob Thornton — but something in the setup feels strained, not quite true, not quite right.

Director David Gordon Green and screenwriter Peter Straughan are going for a tone here, a mix of the outlandish and the real, a sort of black comic welcome to a land where anything goes. The attempt is to create a reality wide enough to accommodate the extremes of absurdity and hard political truth, but the pieces never cohere, and so we end up with a rattling bag of disparate elements.

"OUR BRAND IS CRISIS" Rated: R Opens today

Bullock herself holds the movie together for a time, and if you want to see evidence of this actress’ skill, don’t see her in a better film in which everything is going well. See her in this one, in which everything is almost going wrong, but it never quite does. From scene to scene, she understands what the movie is supposed to be, and so she finds a tone, from the very first seconds, of balancing comedy and drama on a knife edge. She finds glimmers of humor in the dramatic scenes and forlorn resignation in the funny scenes. It’s as if she’s standing in the middle of two sliding doors that are stuck, and she’s trying to force them back together with her bare hands.

Bullock rewards both attention and inattention. You can enjoy the light surface or see the rueful underpinnings that give her lightness a hint of something mysterious. At the start of the film, Jane (Bullock), a political consultant known for being tempestuous, gets dragged back into the business after a few years of hermetic seclusion — and Bullock lets you see that this is a woman who really did need a break. Once in Bolivia, she becomes sidelined by altitude sickness, but then springs to life when she sees a way to put over her candidate.

Her team has the task of trying to elect a politician (Joaquim de Almeida) with no intrinsic warmth, so instead of pretending that he’s cuddly, they present him as the tough Daddy needed in a crisis. That means selling the notion that the country actually is in crisis — hence, the title.

To the extent that "Our Brand is Crisis" deals with campaign machinations, it’s on solid ground, but when it tries to make something zany of the rollicking world of campaign consultants, it’s both unconvincing and tiresome. But the greatest weakness of the film is where it should be strongest, in the relationship between the rival consultants, played by Bullock and Thornton. Jane’s competition with him drives the plot, and one gets the feeling that every time they meet, we should be seeing a clash of titans. But their interaction isn’t particularly clever, and most of the time it’s just dispiriting.

The problems are compounded by an ending that is hard to buy, not only in terms of story but in the direction it steers the main character. "Our Brand is Crisis" is in that annoying category of movie that sends audiences away thinking, "It’s almost good, but something is off."

Review by Mick LaSalle, San Francisco Chronicle