President Donald Trump ordered the National guard to deploy to the Mexican border Wednesday. The last three presidents have summoned the military to the border — with mixed results.

President George W. Bush dispatched 6,000 National Guard troops in 2006. Over a two-year period, those troops helped repair roads, built border fencing and created about 100 miles of border vehicle barriers.

Under President Barack Obama, 1,200 troops were sent to the border after the murder of a prominent Arizona border rancher, Robert Krentz. 

"Since the military and the national guard cannot engage in law enforcement activities by law, they were mostly in a supportive role," said Eric Olson with the Woodrow Wilson Center’s Latin America program.

He expects the Guard will play much the same role in the latest call for a border mobilziation.