By Morgan Lee NOGALES, Ariz. (AP) — Inside an armored vehicle, an Army scout uses a joystick to direct a long-range optical scope toward a man perched atop the U.S.-Mexico border wall cutting across the hills of this Arizona frontier community. The man lowers himself toward U.S. soil between coils of concertina wire. Shouts ring out, an alert is sounded and a U.S. Border Patrol SUV races toward the wall — warning enough to send the man scrambling back over it, disappearing into Mexico. The sighting Tuesday was one of only two for the Army infantry unit patrolling this sector of the southern border, where an emergency declaration by President Donald Trump has thrust the military into a central role in deterring migrant crossings between U.S. ports of entry. “Deterrence…