A member of the National Guard checks on his colleague inside a Border Patrol Skybox near the U.S.-Mexico border in Hidalgo, Texas, in 2011. President Trump is calling for troops on the Southern border, something the past five presidents have all done on a limited basis.

A member of the National Guard checks on his colleague inside a Border Patrol Skybox near the U.S.-Mexico border in Hidalgo, Texas, in 2011. President Trump is calling for troops on the Southern border, something the past five presidents have all done on a limited basis.