During the 2016 election, a new term entered the mainstream American political lexicon: "alt-right," short for "alternative right." Despite the innocuous name, the alt-right is a white-nationalist movement. Yet it differs from earlier racist groups: it is youthful and tech savvy, obsessed with provocation and trolling, amorphous, predominantly online, and mostly anonymous. And it was energized by Donald Trump's presidential campaign. In Making...