“Zero Dark Thirty”—directed by Kathryn Bigelow and produced by Mark Boal—is as divisive and charged as any Hollywood film in memory. “The Hurt Locker,” their film about the Iraq war, won six Oscars in 2009 and broad acclaim. This time the pair are having to defend their work against political attack—in Hollywood and Washington. The controversy has pushed the film, an early Oscar front-runner that has grossed nearly $100 million so far, out of the conversation about likely winners.

“Our movie was hijacked for political purposes,” says Mr. Boal, who wrote the script based on his own reporting. One of the movie’s Oscar nominations is for best original screenplay. Over a late lunch in Venice Beach earlier this week, the 40-year-old native New Yorker is funny, impassioned, defensive and irritated, sometimes in the same sentence.

“We tried to avoid partisanship—I couldn’t have tried harder to avoid partisan politics,” he says.

He seems to have failed. “No doubt,” he shoots back.