As a filmmaker, Sean Baker has built a cohesive body of work around stories from the margins of society. Well, one very particular margin: sex work.

Baker’s 2015 breakout film, “Tangerine” – shot, evocatively, on iPhones and focusing on a transgender sex worker in Hollywood – followed 2012’s “Starlet,” about the unlikely friendship between a porn actress and an elderly retiree. After that came Baker’s most mainstream movie yet: “The Florida Project,” which earned Willem Dafoe a 2018 Oscar nomination for his performance as a kindly motel manager trying to keep a struggling single mother from backsliding into prostitution, a stone’s throw from Disney World.

Baker has been rightly singled out for doing something all too rare in Hollywood: making movies about the often impoverished members of the American underclass, while scrupulously trying to avoid judgment. But with his latest, “Red Rocket” – the story of a washed-up porn actor – the filmmaker may have crossed the line. The film, whose title may or may not refer to a slang term for a dog’s erection, often teeters between compassion and something that feels perilously close to cultural voyeurism.

Simon Rex stars as the triple-X actor known as Mikey Saber, who comes skulking back, battered and bruised, to the featureless contours of his estranged wife Lexi’s dingy home in Texas City, Texas, after unspecified humiliation in the San Fernando Valley, the capital of the adult-film industry. Mikey talks Lexi (Bree Elrod), his former porn colleague, into letting him crash at the home she shares with her disapproving mother, Lil (Brenda Deiss). It helps a little that he’s a charming liar, but more so that he contributes to the rent, with money earned from selling drugs to workers from the nearby oil refinery, in whose grimy shadow the film takes place.

Simon Rex, left, and Suzanna Son in “Red Rocket.” A24 Films

Rex’s performance is equal parts charismatic and creepy – and for the same reason: While he’s using Lexi (and having robust if loveless sex with her to convince her that he wants to patch things up), he’s simultaneously grooming a barely legal 17-year-old cashier at a doughnut shop named, of all things, Strawberry (Suzanna Son).

Grooming for what? Well, sex, at first, but ultimately to become his new adult-film protegee. If the prospect of a grown-up man hitting on, having an affair with and recruiting a teenager for sex work doesn’t seem like comedy material, maybe “Red Rocket” isn’t for you. (Mikey is only technically a grown-up: Rex is 47, but his character acts like he’s 19.)

And yes, the movie plays, at times, like a comedy, despite some dark turns. Mikey’s friendship with a young neighbor named Lonnie (Ethan Darbone), whom Lexi used to babysit, takes a nasty turn. After Mikey causes a horrific traffic accident, he lets Lonnie take the blame for it. There’s not just a sour aftertaste to this story, but a sour before-taste. And in this movie, Baker can’t seem to decide whether he wants us to laugh at, to pity or to understand his subjects. Set in summer 2016, with the Republican National Convention taking place on TV in the background, the movie seems to be making some kind of “Hillbilly Elegy”-style point about Trumpism, but it’s unclear what that point is.

Characters like Lil, who watches trash-TV religiously, and Lonnie, who turns out to be faking a history of military service, seem ripe for mockery, though they’re nicely portrayed by nonprofessional actors, as is Baker’s frequent habit. Alone among the supporting characters, only the daughter of Mikey’s drug supplier (Brittney Rodriguez) seems to have any dignity.

Rex and Son have screen presence in spades. It’s easy to believe their characters could make a go of it in movies. But in this one, they just seem cut out for a different kind of porn: one that delivers titillation at the expense of someone else’s misery.