The apartment building where Daniel Baker was arrested Jan. 15 in Tallahassee. The FBI charged him with using interstate commerce to threaten to injure or kidnap right-wing protesters he thought were planning to attack the Florida Capitol. (Charlotte Kesl/For the Washington Post)

TALLAHASSEE — Shortly after sunrise on Jan. 15, FBI agents descended with guns drawn on a squat, red-brick apartment complex here, broke open the door of one of the units and threw in a stun grenade, prompting the frightened property manager to call 911.

Inside the apartment, furnished with little besides books and a sign declaring “THE REVOLUTION IS NOT A PARTY,” the agents found their target: a 33-year-old U.S. Army veteran and self-described “hardcore leftist” who had posted a flier on social media threatening to attack “armed racist mobs WITH EVERY CALIBER AVAILABLE.” A shotgun and handgun were found in his apartment, they said.