Barry Levinson's political comedy wrestles half-heartedly with a good idea: that a sharp comedian running for President might upstage the hypocritical candidates from the two main parties in those flabby television debates during which nothing much is said and appearance is all.

Robin Williams is Tom Dobbs, the comedian who is persuaded to run and then trumps the aces that both Republican and Democratic candidates have up their sleeves.

Williams's presence is always a mixed blessing, but at least the screenplay gives him some shrewd lines with which to destroy the status quo. But would the comedian actually win?

Here Levinson hedges his bets by having the voting system go wrong and giving him the Presidency by error. The electoral supervisors have been warned about the flaws in the system by Laura Linney's consultant but refuse to admit their mistake - so it's up to Dobbs, who fancies her, to tell the truth to the nation.

The best performance comes from Christopher Walken as Dobbs's amusingly cynical agent.

And its better moments have the edge of good satire. But in the end the film is too compromised to be more than a reasonably pleasurable entertainment, as if it is scared about what it is saying about the American political process.