FILE - In this Nov. 17, 2008 image, a man lies dead after a shootout in Tijuana, Mexico. To many Republican presidential contenders in Thursday, Aug. 8, 2015 debate, the U.S. border with Mexico must be secured for millions in the country illegally to stay. To many commuters at the nation’s busiest crossing, their border already is secure - even thriving by historical standards. (AP Photo/Guillermo Arias)