As “Man of the Year” opens, Robin Williams’ Tom Dobbs gets asked by a member of his talk-show audience why he won’t run for president; the question spawns an Internet campaign urging him to run, and eventually he decides to jump into the race.

Dobbs decides to use the opportunity to force serious discussions of the issues – despite contrary advice from his manager, Jack Menken (Christopher Walken), who wants him to campaign with the boldly irreverent and laugh-producing style of his late-night talk show. But when he is allowed to participate in a debate with the traditional candidates, Dobbs finally embraces his stand-up comic roots. Ignoring the rules and the moderator, he goes on a tirade sprinkled with snappy one-liners that whips the crowd into a frenzy. After that, Dobbs’s grass-roots campaign takes off.

The big message of the movie – oh, what a fine line there is between politics and entertainment! – is a familiar one in a universe where the Terminator occupies the California governor’s office and fans are petitioning for Oprah to run for president. It’s not fresh turf, but it’s still fertile ground for humor. Then the film shifts.

For the first half-hour, you get Williams doing his trademark stand-up and a script that skewers politicians as surface-over-substance and the political process as cheap cabaret. Then comes an electronic voting controversy. And corporate greed. Enter an Enron-like, morals-free company and one eager-beaver whistle-blower (Laura Linney). Witness stalkings and car chases.

“Man of the Year” is a movie that can be smart-funny and astutely topical. But if what you’re expecting is a start-to-finish laugh fest, beware: This picture takes some detours and never really figures out what kind of movie it wants to be.