In a television interview near the end of his life, Roy Cohn predicted that his obituaries would lead with Senator Joseph McCarthy. He wasn’t wrong. Thanks partly to the televised Army-McCarthy hearings, Cohn’s role as the Wisconsin senator’s youthful counsel was imprinted on the public memory and seemed, when Cohn died of AIDS in 1986, to be the most significant episode in a contentious public career.

Lately, the emphasis has shifted, in part thanks to Cohn’s association, in the ’70s and ’80s, with the New York real estate developer who is now the president of the United States. Matt Tyrnauer’s compact and informative new documentary, “Where’s My Roy Cohn?,” quotes President Trump in its title. The film’s answer to the question suggests that Cohn is among the threads that link the politics of the Red Scare with whatever it is we’re living through now. He’s still around.