Yoni Appelbaum’s grandfather was a mailman. Appelbaum shared this fact with me in Charlottesville last week, onstage at a “Democracy360” event hosted by the University of Virginia and cosponsored by The Atlantic, where he is an editor. We were there to talk about “building the American dream” and, by Appelbaum’s account, being a mailman was once a way to do that. “He was proud of that job. And it was enough, together with my grandmother’s job, that they could buy a row house in Canarsie and raise a family.”That was not, however, the point of the story. Rather, Appelbaum wanted...