Politics is always the art of the possible. Compromises are necessary to get candidates elected and legislation passed. The hope is that the dark side of these activities will be justified by the importance of a larger cause. It's often a difficult piece of moral calculus.

Primary Colors is a deft political satire that starts out by tackling these issues head-on. Based on the best-selling novel by New Yorker magazine staffer Joe Klein (who first published the book under the pseudonym, “Anonymous”), the movie claims to be fiction. But, of course, everyone knows it's based on Bill Clinton's 1992 presidential campaign. Part of the fun is figuring out who the real-life models for each of the characters are and how closely the plot twists resemble actual events. Its scenes about the fallout from the candidate's alleged affair with a very young girl seem to have anticipated the Monica Lewinsky scandal with an eerie prescience.

The story is told through the eyes of Henry Burton (Adrian Lester), who's a cross between former Clinton aide, George Stephanopoulos, and a mythical grandson of Martin Luther King, Jr. The young African-American signs on to be campaign manager of a dark-horse, Clinton-like presidential candidate, Jack Stanton (John Travolta), who's governor of a small Southern state.

Burton's girlfriend, March (Rebecca Walker), describes Stanton as “some cracker who hasn't done much in his own state.” But the young idealist explains to Stanton's Hillary-like wife, Susan (Emma Thompson) why he joined up: “You had Kennedy. I want to be part of something that is history.”

Stanton has the hubris to see himself as following in Lincoln's footsteps.

From that moment on, Burton is pegged by the rest of the staff as suffering from a case of “galloping true believerism.” The movie's dramatic tension comes from the clash between his high hopes and the reality of the campaign. It's a classic tale of innocence betrayed.

Burton first sees Stanton in action at a minority adult literacy class in New York. The candidate is moved to tears by the students' tales of hardship and shares with them a similar story from his own past. But he can't resist seducing the group's female teacher (Allison Janney).

The incident reveals the candidate's greatest strength, his seemingly heart-felt empathy for ordinary people's problems. But it also points to his achilles heel, what's described as “the woman thing” by veteran consultant Richard Jemmons (Billy Bob Thornton), who's based on James Carville.

The New Hampshire electoral primary takes up the first half of the film. The Stanton campaign has to deflect charges that their candidate was arrested during a Vietnam war protest and had the incident illegally expunged from his record. Then allegations are made that he had an affair with his wife's former hairdresser (Gia Carides), a character suggested by Gennifer Flowers, and a tape recording is played which seems to prove it.

Susan Stanton publicly stands by her man and leads the campaign's rapid-response team to media inquiries. But in private, she slaps her husband's face upon learning of his infidelity and later pulls her hand away from his after faking forgiveness during a 60 Minutes-like TV interview. Her attitude toward her husband seems to be an accurate rendering of the combination of true love, anger, and denial that binds her real-life counterpart to the president.

Brought in to counter the dirty tricks of Stanton's opponents is “dust-buster” Libby Holden (Kathy Bates), based on long-term Clinton associate, Betsey Wright. A foul-mouthed homosexual, she's not above using threats of violence to get her way. With Holden's help, Stanton is able to neutralize the allegations made against him and finish second in New Hampshire. When the candidate who beat him drops out for health reasons, he becomes the front-runner.

Then things take a turn for the worse. Rumors surface that he has gotten a teen-age African-American girl pregnant. At the same time a respected party veteran, former Florida governor Fred Picker (Larry Hagman), enters the race to run against Stanton on a good-government platform.

Burton gets his hands dirty dealing with these problems and feels sick about it. Surprisingly, Holden turns out to be as much an idealist as he is. After finding enough skeletons in Picker's closet to force him out of the race, she challenges the Stantons to remain true to their shared McGovernite past and not stoop to their opponents' level by releasing the material.

The problem with Primary Colors is that both director Mike Nichols (The Graduate and Birdcage) and screenwriter Elaine May (Birdcage) are liberal Democrats who've participated in Clinton fund-raisers, and three-quarters of the way through the film they realize the Clinton surrogate they've created is a monster. Jack Stanton is depicted as a charming manipulator who'll use any means necessary to accomplish his goals. He functions as a kind of Mephistophelean tempter with Burton, encouraging the young man to do things that go against his nature. After all this, how are the filmmakers going to be able to justify their support for the movie's real-life model and for the principles they and he claim to hold dear?

In its closing scenes, the movie ceases being funny and bogs down in exaggerated melodrama and unconvincing moral rationalizations. Nichols and May want us to believe that almost all of America's presidents have used dirty tricks. Delivering some of the most offensive lines of dialogue in recent memory, Stanton tries to persuade Burton to stay on board. “You don't think Abraham Lincoln was a whore before he was president?” the candidate asks. “He had to tell his little stories and smile his back-country grin. He did it all just so he'd get the opportunity to stand in front of the nation and appeal to the better angels of our nature.” Obviously, Stanton has the hubris to see himself as following in Lincoln's footsteps.

Because Primary Colors shows the Stanton campaign concerned almost exclusively with image and rarely with substance, there's very little sense of a higher cause to justify all the chicanery. In order for the audience to accept Stanton as anything other than a wily corrupter, the filmmakers are forced to fall back on a blanket cynicism about politics that makes their hero look good. Despite all the laughs, it leaves a bitter taste.

Arts & culture correspondent John Prizer writes from Los Angeles.

Primary Colors is rated R by the Motion Picture Association of America.