Del Harris is a man whose calm, composed exterior belies a war going on inside.

As played by Jeff Daniels (“The Newsroom,” “Steve Jobs”) in the Showtime drama series “American Rust,” premiering Sunday, Sept. 12, he’s the chief of police in Buell, Pa., a forlorn Rust Belt town outside of Pittsburgh that’s pockmarked by deserted factories and empty, decaying buildings.

A veteran of the war in Iraq, he takes a cocktail of opioids to keep his PTSD at bay but struggles with maintaining the diminishing dosages his doctor prescribed. He has a love interest in Grace (Maura Tierney, “The Affair”), but she also has an ex-husband who won’t go away and a son, Billy (Alex Neustaedter, “Colony”), who has a propensity for getting into trouble after turning down a football scholarship and getting dumped by the love of his life, Lee (newcomer Julia Mayorga).

But despite everything, Del still pines for Grace and is protective of Billy, even stepping in to get the kid probation after he clubbed a guy with a board in a bar fight. But when a dead body turns up in an abandoned mill and Billy is implicated, Del must decide the lengths to which he will go to protect the son of the woman he loves.

Based on the novel by Philipp Meyer, the series is the story of good people making bad choices in places that progress seems to have left behind, the type of people that Daniels, a native Michigander, knows well.

“I am one of those folks that comes from a part of the country that can feel less, can feel inferior, the fly-over country, the you’re-not-from-the-coasts,” the actor explains. “So I understand that. I’d lived with it as an actor going in and sitting in waiting rooms against people from Yale and Juilliard and the Royal Academy of Dramatic Arts. I understand those people and that person.”

Del’s relationship with Grace is reflective of that. He clearly cares for her but she seems on the fence about him, and when he sees her with her ex, he backs off. But Daniels’ working relationship with Tierney is the opposite. He praises his co-star for being a smart actress, a worthy acting partner and someone who “jumped off the cliff with me” in terms of making acting choices.

“I’ve always said half my performance is in the other actor, which is another way of saying listen and react,” Daniels says. “And if you do that, you’ll have chemistry but you can’t do that with someone who’s just waiting for you to stop talking and then is going to do whatever they’re going to do. Maura didn’t do that. Maura said, `Oh, OK, I get it,’ and jumped in. … Now you’ve got that thing they call chemistry and that happened early on with us.”