How does darkness overtake a nation? The philosopher Hannah Arendt took up the subject in her book “Eichmann in Jerusalem,” which investigated the mystery of how ordinary Germans transformed into murderous Nazis. The face of evil, Arendt discovered, wasn’t a demon lurking in the cellar but the factory supervisor in the nice house across the street. Those carrying out the orders that led to the extermination of millions of Jews along with other marginalized groups became part of the bureaucracy of genocide. This startling and still controversial insight — that the Holocaust was executed not by sadists but by conformist clerks and self-interested middle managers — inspired the famous subtitle of Arendt’s book: “A Report on the Banality of Evil.”Robert Schenkkan, the Pulitzer Prize-winning playwright (“The Kentucky Cycle”) who co-wrote the screenplay for “Hacksaw Ridge,” has a new play that explores the concept of the banality of evil in our own backyard. “Building the Wall,” which opened Saturday at the Fountain Theatre, imagines the unimaginable happening in Trump’s America. To read more, click here.