The latest Sean Penn romp tells of a loner whose self-obsession hovers somewhere between mentally challenged nerdhood and insanity. Apart from this trifling coincidence, The Assassination of Richard Nixon is about as far from 2003’s Mystic River as you can get, although both feature the trademark plonking intensity/humourlessness Penn brought to this year’s Oscars shindig. It’s not that the guy can’t act. He can. But in Nixon, Penn and his director Niels Mueller seem to actively beg the question: how dark can you make both the performance (and sets) before a movie becomes unwatchable to an audience not composed exclusively of manic-depressives and eagle-eyed owls? The answer is very, very dark indeed.

In early 1974, Sam Bicke, a divorced father with a John Waters moustache and a nightmarish job selling office furniture, hatches a plot, of sorts, to hijack a plane and ram it into the White House – convincingly nutty at the time if less so today. As with 1973’s The Day of the Jackal, which concerned the plot to assassinate De Gaulle, the film inevitably loses zing given the recorded facts – I’m pretty sure the much maligned 37th President left town in a Marine helicopter, not a fiery explosion.

Instead, we’re asked to sympathise with the lead, an otherwise harmless cove allegedly driven bonkers by Watergate, capitalism and too many TV dinners: much the same sort of schlub, Mueller posits, as Nixon himself. At one stage Bicke dons a Santa Claus suit the better to ‘publicly petition my government for a redress of grievances’ (in historical fact, his being denied a federal loan to open up a tyre store in the back of a derelict school bus). The craziness mounts, as does the feeling that one should have stayed home and rewatched the DVD of Taxi Driver. Penn himself apparently disdains the comparison with Scorsese’s 1976 cult classic, but it’s inescapable, right down to the two protagonists’ names: Bicke. Bickle. You be the judge.

In real life, the Penn character was a paranoid thug who murdered a Maryland police officer named George Neal Ramsburg who had the misfortune to be on duty in Baltimore-Washington International Airport on 22 February 1974, then vaulted over the body into a loading jet where he shot and killed one pilot and wounded another before himself being taken out by police. Somehow, Bicke’s victims don’t rate a namecheck in this particular movie. Entertainment-wise, The Assassination of Richard Nixon is towards the back of a crowded field led by the likes of 1993’s Falling Down and the original 1962 Manchurian Candidate. Morally, it’s a non-starter.