Stewart Rhodes was living his vision of the future. On television, American cities were burning, while on the internet, rumors warned that antifa bands were coming to terrorize the suburbs. Rhodes was driving around South Texas, getting ready for them. He answered his phone. “Let’s not fuck around,” he said. “We’ve descended into civil war.”

It was a Friday evening in June. Rhodes, 55, is a stocky man with a gray buzz cut, a wardrobe of tactical-casual attire, and a black eye patch. With him in his pickup were a pistol and a dusty black hat with the gold logo of the Oath Keepers, a militant group that has drawn in thousands of people from the military and law-enforcement communities.

Rhodes had been talking about civil war since he founded the Oath Keepers, in 2009. But now more people were listening. And whereas Rhodes had once cast himself as a revolutionary in waiting, he now saw his role as defending the president. He had put out a call […]