The story of Milo Yiannopoulos’s fall from conservative grace ended when a conservative blog posted video footage of him making comments that seemed to rationalize pedophilia. But it started when a 16-year-old high school student in Canada decided Yiannopoulos was embraced much too closely by mainstream conservatives. The teen was moved to dig up footage on Yiannopoulos when she heard that he’d been invited to speak at the highest profile gathering of conservatives each year in America, the 2017 Conservative Political Action Conference (CPAC). She defines herself as “very socially liberal,” but leans right on economics and foreign policy. Yiannopoulos,...