In late August, the constable in a small county outside Fort Worth logged on to his Facebook account and called for the execution of a mayor nearly 2,000 miles away.

"Ted Wheeler needs to be tried, convicted and executed posthaste," John D. Shirley wrote on Aug. 31. "He has blood on his hands, and it's time for justice." What precipitated Shirley's outburst against the mayor of Portland, Ore., was the shooting death on Aug. 29 of a member of a right-wing group called Patriot Prayer by an antifa activist. The killing was a violent escalation of clashes that had roiled Portland in the weeks since George Floyd was suffocated to death by police. Shirley said "patriots" in "socialist-controlled cities" needed to protect themselves. As the presidential election approached, he warned of "open conflict." Twitter suspended his account shortly after, but he continued to post about violent disputes on Facebook with crescendoing alarmism.