From certain angles, director Matt Tynauer’s sharply crafted documentary on the late N.Y.C. über-lawyer Roy Cohn plays like an American horror story, melting into modern-day horrors. The shamelessly and socially suave Machiavellian Cohn, who died of AIDS in 1986, was associated with many of the dubious aspects of the second half of the 20th century — including the McCarthy “witch hunt,” helping send the Rosenbergs to their death, political tinkering across decades, Mafia coddling, and mentoring Donald Trump, to whom he offered such sage advice as “never admit you’re wrong, never apologize.” Drawing on a rich supply of archival footage, and many interviews with Cohn, his allies, and enemies, Tynauer appeals to our fascination with scoundrels, while painting a portrait of a possibly amoral titan of sleaze, with friends in high places. Take, for instance, the current White House.