At the southern border, a do-it-yourself approach to security

The Border Patrol operates according to a “shift mentality,” their responsibilities limited by time and distance, he said. Many agents are assigned to the station in Tucson, more than an hour away. “When they’re coming down,” Mr. Foley said, “they’re being reactive” to an image on a video camera or a ground sensor set off by someone where no one should be.

“They’re already behind,” he said. “What we do is try to be proactive.”