Border Security Remains Key Issue In Presidential Campaigns [Getty Images]

RIO GRANDE CITY, TX - DECEMBER 07: Immigrants walk handcuffed after illegally crossing the U.S.-Mexico border and being caught by the U.S. Border Patrol on December 7, 2015 near Rio Grande City, Texas. Border Patrol agents continue to capture hundreds of thousands of undocumented immigrants, even as the total numbers of those crossing has gone down. (Photo by John Moore/Getty Images)

Getty Images News John Moore