Two weeks before chaos hit St. Luke's hospital in Boise, Idaho—before Ammon Bundy showed up with an armed mob and the hospital doors had to be sealed and death threats crashed the phone lines—a 10-month-old baby named Cyrus Anderson arrived in the emergency room.

The boy's parents, Marissa and Levi, knew something wasn't right: For months, Cyrus had been having episodes of vomiting that wouldn't stop. When he arrived in the ER, he weighed just 14 pounds, which put him in the .05th percentile for his age. Natasha Erickson, the doctor who examined him, had seen malnutrition cases like this in textbooks but never in real life. Cyrus's ribs were clearly visible through his chest. When he threw up, his vomit was bright green.

Erickson hooked the baby up to an IV and a feeding tube, and he slowly started to gain weight. But Levi and Marissa were anxious to leave. They were members of an anti-government activist network that Bundy, the scion of America's foremost far-right family, had founded, and they shared his distrust of medical and public-health authorities. To Marissa—whose father, Diego Rodriguez, is himself an extremist leader and Bundy's close friend—the hospital was a "lion's den."