The causes of America’s resurgent tribalism are many. They include seismic demographic change, which has led to predictions that whites will lose their majority status within a few decades; declining social mobility and a growing class divide; and media that reward expressions of outrage. All of this has contributed to a climate in which every group in America—minorities and whites; conservatives and liberals; the working class and elites—feels under attack, pitted against the others not just for jobs and spoils, but for the right to define the nation’s identity. In these conditions, democracy devolves into a zero-sum competition, one in which parties succeed by stoking voters’ fears and appealing to their ugliest us-versus-them instincts.