How to effectively satirise a world in which Donald Trump is President vexes some of the greatest minds of the artform. 

Almost a decade after Four Lions, Chris Morris, who undoubtedly fits that ‘greatest minds’ description, has chosen to tell a version of a terrifyingly true story to highlight the very personal cost of a politics that places spin ahead of principle.

The Day Shall Come is, we are told, based on 100 true stories, and most closely the case of the Liberty City Seven, in which a terror cell accused of planning to bring down the Sears Tower in Chicago were actually a rag-bag of delusional, impoverished Haitian Catholics whose grand plan was to ride into the city on horseback. 

They had been entrapped by FBI officers who offered them all the money to fund the crackpot scheme. All very laughable, except for the fact that the alleged ringleader,  after several retrials, is now serving 13 and a half years behind bars.

Morris’s fictionalised version of these events revolves around the Star Of Six, a tiny, impoverished black commune in Miami, led by Moses Al Shabaz.

Though his tiny group of followers swear off guns, they hope to overthrow the white man by channelling the will of God and his prophets, including ‘Black Santa’, and summoning the CIA’s secret army of dinosaurs. The big man told him so himself, communicating via a duck. 

That this supposed revolutionary force is hapless is where similarities to Four Lions end, for the focus of The Day Shall Come’s is as much on the FBI’s manipulative methods and the serious consequences of their operation than it is on the supposed terrorists.

Moses gets drawn into their dangerous, self-serving games when his absurd but fiery calls for upheaval come on to the radar of ambitious agent Kendra Glack (Anna Kendrick on fine form). She sets him up with a bogus Al Qaeda representative who offers to supply him all he needs, using paedophile Nur Ad-din (Kayvan Novak) as a go-between. The feds’ plan is to bust the ‘cell’ once Moses falls for it.

This escalates into the Star Of Six supplying what they believe is radioactive uranium to a neo-Nazi cell led by a guy called Lemmy (comic Jim Gaffigan falling surprisingly naturally into the role) and a full-on nuclear emergency.

Probably because of the severity of the subject matter, the tone of The Day Shall Come is rather uneven, swaying from clear comic moments to spine-chilling realities. 

The delusion of the supposed revolutionaries is clearly bizarre – even if underpinned by mental illness and genuine injustice that’s harder to laugh at. And some eviscerating, point-scoring banter between the super-cynical FBI agents and other law enforcement figures is sharply acidic. That’s no surprise since the film’s co-writer, Jesse Armstrong, wrote on The Thick Of It and Morris has directed a few episodes of Veep, though the insults are never quite as stringing as on TV.

But the comedy, however dark, always sits well with the more dramatic scenes or the political point-making, especially as the FBI’s stitch-up escalates. 

Moses, too, is a mass of contradictions. We have to see him as absurd yet serious; as a soft-bellied family man who eschews violence in his fight for black rights, yet who’d sell WMDs to white supremacists without much hesitation.  It’s a credit to relatively little-known Marchánt Davis that he keeps all this together in a watchable, if strange, performance from which a naive tenderness emerges.

Morris certainly succeeds in using satire to throw some light onto the shady operations of the FBI, but whether The Day Shall Come succeeds as a gripping, convincing story or astute comedy is mooter. But there’s plenty of food for thought generated from the subject matter.

• The Day Shall Come is on general release from today.