....protecting the candidates is no game — it comes with the territory that an agent may have to take a bullet for the president or a candidate.

The actual instruction to Secret Service trainees is a little more complicated. “What we are trained to do as shift agents is to cover and evacuate if there is an attack,” an agent says. “We form a human shield around the protectee and get him out of the danger area to a safer location. If an agent is shot during the evacuation, then that is something that is expected. We rely on our layers of security to handle the attacker while the inside shift’s main function is to get the heck out of Dodge.”

The idea is to never allow an attack to happen in the first place. The key to that is the Secret Service’s James J. Rowley Training Center in Laurel, Md. ....