Colorado mother Cynthia Abcug became an unlikely star on the fringe right last year thanks to a battle with her state’s child-welfare department over custody of her son, which became a cause célèbre among believers of the bizarre pro-Trump QAnon conspiracy theory. According to a heavily redacted police affidavit, Abcug’s daughter told police that her mom was a committed QAnon believer who had been discussing how “people from the Q-Anon group planned to kidnap” the unnamed person. Abcug had obtained a gun of her own, according to her daughter, and talked about a person or group of people “dying” in...