Charlie Kirk, the conservative influencer who was assassinated in September, and Nick Fuentes, the young Hitler-loving white nationalist at the center of a growing schism on the right, were bitter enemies. Fuentes despised Kirk for his support of Israel, and, more broadly, for his efforts to marginalize Fuentes’s gleefully racist and fascist brand of politics. In 2019, seeking to expose Kirk as “anti-white” and a “fake patriot,” Fuentes organized his army of young fans — known as Groypers, after a variant on the alt-right Pepe the Frog meme — to flood events held by Kirk’s organization, Turning Point, and ask...