George Clooney’s “Suburbicon” has a timely subplot — based both on present times and a 1957 incident — about racism in white America. That subplot, however, resounded deeply during the Venice Film Festival press conference for the film, which stars Matt Damon and Julianne Moore. “I was watching a lot of speeches on the campaign trail about building fences and scapegoating minorities and I started looking around at other times in our history when we’ve unfortunately fallen back into these things,” said Clooney, talking about how the pic germinated. While casting around for story ideas, Clooney found a 1957 incident...