Early last year, a young neo-Nazi called his girlfriend from a jail cell in Phoenix. She was upset. She was confused. She wanted to know why FBI agents were in her living room saying they caught him making pipe bombs and stockpiling other explosives.

“Why were you guys making that stuff?” she asked. “Why did you have it in your truck?”

“Because,” he told her, “we wanted to make those things for the border.”

By all accounts, Jeffery Harbin was a minor player in the white supremacist movement, a man living deep in the fringes of American extremism. But in the broader context of the immigration debate, he was hardly alone.