Nick Offerman & Dennis Quaid in Timely Drama

It’s been a particular pleasure to watch the blossoming of Nick Offerman’s acting career in recent years. The actor, who rose to fame with his hilariously droll performance as Ron Swanson in the hit series Parks and Recreation, has never stopped working. But his talent has really risen to the fore lately, especially with his heartbreaking, Emmy-winning guest appearance in HBO’s The Last of Us.

Now, with Christian Swegal’s feature debut Sovereign — receiving is world premiere at the Tribeca Film Festival before its theatrical release later this month — he’s been given his meatiest film role to date. And boy, does he run with it.

He’s playing a role for which he has some previous experience. In Parks and Rec, his character was an anti-government libertarian. But what he played for comedy then is now deadly serious in this drama inspired by real-life events. The film, set in Arkansas in 2010, tells the story of Jerry Kane, a self-described “sovereign citizen” who proselyted against laws and governmental authority via appearances on right-wing radio talk shows and traveling around the Midwest delivering seminars about property rights and avoiding taxes. It’s as if Ron Swanson had gone fully around the bend.

A widowed, unemployed roofer, Jerry constantly faces eviction and home-schools his teenage son Joe (Jacob Tremblay, Room). He’s a loving but disciplinary father, hectoring his son to say his prayers every night and reminding him, “Don’t forget J.C.” Like many others of his ilk, he fervently believes in gun rights, illegally owning an AR-15 that gets him into trouble when he and his son are pulled over for a routine traffic stop.

He’s promptly arrested, with Joe being temporarily placed in a juvenile home, where he begins to feel some relief from his father’s relentless intensity. The local police chief, John (Dennis Quaid, infusing his portrayal with low-key gravitas), understatedly tells Joe, “It sounds to me like your dad doesn’t like the government so much. He has some…interesting ideas.” When Jerry is bailed out several days later by his on-and-off girlfriend Lesley Anne (Martha Plimpton, warmly affecting), he’s even more extremist than before, threatening to sue the cop who arrested him, refusing to recognize the authority of the court, and walking out of the courtroom during his trial.

Director-screenwriter Swegal intercuts the story of Jerry and his son with scenes involving the police chief and his grown son Adam (Thomas Mann), who’s training to be in the force. Their relationship is loving but tense, with John constantly lambasting his son for such things as picking up his newborn baby whenever he cries. For a long while it’s hard to understand why the narrative is split in such separate directions, until the stories fatefully intertwine in the film’s shattering climax.

Timelier than ever in its portrait of a radicalized margin of society rebelling against governmental authority, Sovereign might have benefited from a little more backstory as to what set Jerry on his non-conformist path. But it nonetheless works well on its own terms, especially in its depiction of the complicated relationships between both fathers and their sons.

Offerman is simply terrific, supplying the outsized charisma necessary to make understandable Jerry’s hold over vulnerable people while conveying the humanity that explains why his son and girlfriend are loyal to him. His character’s tough-love approach is effectively dramatized in a digressive but powerful scene in which he gently but firmly forces Lesley Anne to confront her terrifying fear of horses. Tremblay, displaying a compellingly intense screen presence, is equally effective as the son who loves his troubled father enough to tragically follow in his footsteps.

Also featuring an unfortunately underutilized (but always welcome) Nancy Travis, Sovereign benefits greatly from its empathetic, non-exploitative approach to its controversial subject matter. It’s uncomfortable but necessary viewing.