“Why don’t you [expletive] off and die?” shrieks Disturbed. The instructors pounce with sticks and training knives. They slam the trainees into the wall. They rip at their hair. One trainee shatters his instructor’s cheekbone. But another freezes, goes into “brain vapor-lock,” as his partner is repeatedly shot.

Krista and her partner wait outside for their turn. “If they clench their fists,” Krista strategizes, “I’ll pull out my baton.”…

“We train unlike any other federal agency,” says A.T. Smith, an assistant director, who stands by while the trainees stencil their names on their T-shirts. “We train to the edge, and then we lean over.”

The center’s drills are increasingly scenario-based, says Smith, who had served as Hillary Clinton’s detail leader. “For years, our training was based on the lone gunman and the long-range rifle. Now it’s automatic weapons, multiple explosions as a diversion to a secondary attack.” An intelligence PowerPoint presentation on “The Emerging Threat” flashes from the old-style assassin, Squeaky Fromme, to chanting Islamic fanatics. Threat experts have created a new Obama-era prototype, a white supremacist who calls Obama “a mud person” and White House Chief of Staff Rahm Emmanuel, a Jew, “the Antichrist.”

New hazards have prompted a new emphasis in training — a kind of extreme, lethal improv — using scenarios that are dynamic and demand responses that run counter to typical human behavior. Smith says, “Our goal is to make it instinct.”