But the Covington story isn’t just a run-of-the-mill incident of viral outrage. It involved MAGA-hat-wearing teens and Native American activists. Those who shared the video in those first 24 hours, including many conservatives, seemed to feel it was emblematic of the vitriol and racism that drives the worst of American culture. But when new details shifted the story into more ambiguous territory, a well-oiled machine of pro-Trump personalities and sites saw an opportunity to strike. For the students and their defenders, attempts by the media to complicate the narrative of the first viral video came too late. Online vigilantes had...