The first time we see Officer Jason Dixon in Three Billboards Outside Ebbing, Missouri, he’s patrolling in his cruiser and crooning a little tune. Soon, he stumbles upon three newly pasted billboards on a quiet country road. The song he’s singing, a cowboy’s lament called “Streets of Laredo,” is more than a century old. It’s a frontier ballad, sung from the perspective of a dying cowboy to a younger man. This lullaby has been covered by dozens of artists over the years, from Johnny Cash to Joan Baez, Marty Robbins to Burl Ives. It’s a reinterpretation of a 19th-century Irish folk song, “The Unfortunate Lad,” which originated the familiar melody you can hear in the British sailor’s anthem “Spanish Ladies” and the New Orleans standard “St. James Infirmary Blues.” In other words, it’s a song larded with history and meaning, recognizable to almost anyone who hears it.

It’s a key song in movie history, too—its lyrics were borrowed for the title of Mark Harris’s 1956 baseball novel, Bang the Drum Slowly, which became a 1973 film starring Robert De Niro. It’s also a totem in the Western genre, inspiring a William Holden film of the same name and playing a pivotal role in the 1948 John Ford oater 3 Godfathers. In that film, John Wayne sang the song on-screen.

That the London-born British Irish playwright and filmmaker Martin McDonagh chose this song to introduce the racist Dixon, played by Sam Rockwell, cannot be coincidental or merely the product of Marty Robbins fandom. The song is an anthem of regret, but also an admission of guilt. “Take me to the green valley, there lay the sod o’er me / For I’m a young cowboy and I know I’ve done wrong,” the song goes. It’s a cry for mercy, and a fitting song for a character seeking renewal who doesn’t deserve it. But like all good folk songs, it morphs as the singer changes. When the Duke sings it, we hear one thing. When Joan Baez sings it, we hear a different experience altogether. “Streets of Laredo” is not a moral statement of purpose.

The same can be said of McDonagh’s movie. After four wins at the Golden Globes on Sunday, Three Billboards has emerged in recent weeks as a kind of de facto Academy Awards front-runner, the beneficiary of an indecipherable season, and subsequently the recipient of a serious backlash. Rockwell’s mantel is piling up, too. Some cultural critics and close watchers of awards season are angered by this turn of events, citing a redemptive arc for Dixon that never portrays his heinous torture of an African American suspect, but attempts to use it as a pretext for a transformation into a vigilante hero by movie’s end. It’s a quagmire of a character, and the way we talk about characters and what they mean has changed radically. Celebrating Rockwell’s performance has become thornier by the day.

McDonagh—whose work on the stage in London and on Broadway has a nervily funny, shock-you violence—is not an insinuator. A character in Three Billboards is seen reading Flannery O’Connor’s A Good Man Is Hard to Find—this man is eventually thrown through a third-story window. Before a fateful bar fight, a jukebox blares “Walk Away Renee” by the Four Tops. The titular billboards—etched in red and black, like satanic hieroglyphs—burn up in the night sky. A man shoots himself in the head, but not before putting a bag over his head with an inscription.

Three Billboards is a ball peen hammer of middle-American angst. The characters are crass, rude, unconscionable. The themes are brazen, unsettling, and irresolvable. Women are raped, police officers are violent, money corrupts, and cancer kills. It’s also darkly comic, with McDonagh’s dry signature cynicism and pipe-bomb punch lines. (“Penelope said ‘begets’?” was one of 2017’s funniest, most efficient lines of dialogue.) Rockwell, a much admired character actor, portrays another in a long line of ne’er-do-wells and vile figures. “When you play antiheroes, psychos, you get a little more leeway,” Rockwell told Vanity Fair recently. The controversy has not proved that out.

Rockwell has had a firm standing in the Oscar race for months, an unsurprising result for a respected actor with an irrefutable résumé who found a film that speaks to a sense of rage in the country. We live in rageful times. Frances McDormand’s Mildred Hayes is the center of Three Billboards, a boiling cauldron of betrayed motherhood, furious and devastated by the police’s inability to find the man who raped and killed her daughter, Angela. Like so many Best Supporting Actor winners before him, Rockwell’s character delivers an eyedropper’s worth of poison, powerful enough to toxify the cauldron and activate the movie. This is the conundrum of Rockwell in the race, and more indicative of the queasiness that the film has inspired.

More than any other category, Best Supporting Actor rewards the unforgivable, the bastard. It’s a wretched hive of villainy and scum. Look at some recent past winners: Christoph Waltz as the gleeful Nazi “Jew hunter” Colonel Hans Landa in Quentin Tarantino’s Inglourious Basterds in 2010. Heath Ledger’s posthumous victory for the Joker before that. Javier Bardem’s dead-eyed butcher, Anton Chigurh, from No Country for Old Men the year before that. Gene Hackman won for his brutal turn as Little Bill Daggett in Unforgiven in 1993. Gig Young won for his cunning MC in 1969’s They Shoot Horses, Don’t They? None of those characters are redeemed. Best Supporting Actor is where monsters thrive. These are parts that let actors flex and have fun, take chances and abandon good manners.

Rockwell’s character is a monster given a chance at focusing his life when he endeavors to find the man who raped and killed Mildred’s daughter. This numbskull, a racist and unthinking man who reads Robot Comics, has been fired from the police force and is cast into exile in the home of his crone mother, from whom he has learned all his worst ideas. Suddenly, he develops a moral compass. After he is badly burned in a fire at the police station (started, crucially, by Mildred), Dixon experiences an act of forgiveness when he shares a hospital room with the man he has thrown from that third-story window. The man, Red Welby, played with a twitchy charm by Caleb Landry Jones, makes a peace offering: a glass of orange juice, with a straw, for Dixon, who is bandaged from head to toe. From that moment, Dixon becomes something different from the buffoonish, ignorant cop working in the same part of the country that witnessed real-life police violence and community outcry little over three years ago. It’s a complicated, vexing character pivot. Ebbing, Missouri, is not a real place, but Ferguson is.

Critics of McDonagh’s movie have called Dixon’s transition from devil to white knight unearned and offensive. They see his arc as dubious movie magic and McDonagh’s insensitive use of race as a chess piece in his dramaturgical game. After watching it two more times this week, I see a slightly different version of the movie than those critics do—not a more empathetic one, just more dissolute. The Globes pitched it as a story of forgiveness and understanding in a hard world—like The Best Years of Our Lives or Terms of Endearment. Critics pitched it as new-school Crash, vindictive and clumsy. When Three Billboards ends, it ends in a kind of ambiguity. Dixon’s sleuthing has led him to a suspect in Mildred’s daughter’s death—but we quickly learn he’s got the wrong guy. The suspect is a rapist, just not Angela’s. Mildred and Dixon are finally united, even in their failure. It occurs to Dixon to take action anyway, to enact a sacrificial killing. Mildred is in; she needs to exercise some violence of her own. If they travel together to Idaho to kill the man they initially thought did it, they can channel the anxiety, sorrow, and fury coursing through their veins. It will be an expression of rage on a level of Greek tragedy—an eye for a blind eye.

The movie ends before we can see what they do, whether they follow through with their pact, as Mildred and Dixon drive together, laughing and growing closer, beginning to understand one another. We root for Mildred, who has survived domestic abuse, raised two children on her own, publicly reckoned with her daughter’s death, and fought through the genial bullshit of life in an effort to be real and heard. She says what she feels, 30 feet high and 50 feet wide. But Mildred is broken, too. She is over the edge, and cannot be retrieved. She kicks teenagers in the crotch, flicks cereal in her children’s hair, swears with an unbound flair, and deflects her son’s pleas for equanimity. Then she lights that police station on fire. She’s more than an asshole—she’s unhinged. In the words of Telegraph film critic Robbie Collin, she’s a grotesque, much like Dixon. Together, they make a monstrous pair, self-appointed avenging angels attempting to extinguish all the fire in hell. McDonagh wrote both roles specifically for McDormand and Rockwell. And together they are, in his eyes, equal.

McDormand also won a Golden Globe on Sunday and could well be the favorite to take home her second Academy Award in March. Her character is not under fire in the way Rockwell’s is. McDonagh said this week, in the aftermath of some of the controversy around the movie, that he does hope and believe that people like Rockwell’s character can change. Though that is not an endorsement of Dixon.

“I think some of [the criticism] comes from the idea that Sam’s character is redeemed at the end of the film, and I don’t think he is,” McDonagh told Variety. “At the end he’s still the asshole he was at the start of the film, but hopefully by the end of it he’s seen that he needs to change. But the film isn’t about simple heroes and villains, and in no way does he become a hero in it. Part of the whole idea of the story is, ‘Who are the heroes and who are the villains and is anyone really that heroic?’ I wanted to explore the idea of a strong woman going against the police in the South, and I think the racial angle is one of the weapons she would throw at them. But the idea that there’s hope in a story like this, even with characters as despicable as Sam’s, I thought that was an interesting thing to explore.”

There’s something poetic about Rockwell becoming famous for a monster. The 49-year-old actor best known for playing slick villains in Charlie’s Angels and Iron Man 2 is beloved for his subtle, complex work in smaller movies like Moon, The Assassination of Jesse James by the Coward Robert Ford, and The Winning Season. He is hosting Saturday Night Live this weekend, a kind of confirmation of his moment and the movie’s. In his work, Rockwell has a wily charm, as quick to flash malevolence as wide-eyed joy. When he plays dumb, it’s in a way that only a smart guy can. In public, Rockwell evinces a smart but jocular personality—he seems like a good hang. But that’s gone when he’s Dixon. That’s why we’re talking about him in the first place.

Unforgiven’s Little Bill Daggett is a despicable villain—he abuses prostitutes and murders men in cold blood. Appreciating Hackman’s performance is obviously not a validation of the character’s twisted point of view. Would Hackman win in this climate? It’s impossible to know. Rockwell’s character is not so clear—McDonagh does not provide an overwhelming empathy for him, but he does offer time and space. The same can’t be said of any black characters in the movie, who operate like blankly noble bellwethers, like Clarke Peters’s Abercrombie, or merely window dressing, like Amanda Warren’s Denise, who is imprisoned for much of the film and played for a pawn in Mildred’s war with the police. They just don’t have the richness of Mildred or of Woody Harrelson’s Chief Willoughby. This is the movie’s great flaw.

That likely will be interrogated with greater depth after the nominations for the Oscars are announced later this month. Rockwell is likely to win in March, capping a string of performances much admired by his peers. And what comes after that? Some fascinating, perhaps unfortunate consistency. His next two characters will make Officer Jason Dixon seem downright ineffectual by comparison—so much so you might think Rockwell’s been typecast. The first comes in first-time director Robin Bissell’s The Best of Enemies, which tells the story of Ann Atwater, a civil rights activist (Taraji P. Henson), and her showdown with C.P. Ellis, North Carolina’s Exalted Cyclops of the Ku Klux Klan. The second will be in Backseat, The Big Short director Adam McKay’s film about Dick Cheney. Rockwell will play President George W. Bush. How’s that for a cowboy’s lament?