Obama sent troops to the border but he never declared it a national emergency.
July 25 2011. Made against the Mexican Cartels, confiscating property and prohibiting entry into the US.
As to the question of wether the president can declare a national emergency Clinton, Bush W, and Obama did it 28 times. Of the 13 times Obama did it, 11 of them are still in effect. One of these was about the water condition of one city, Flint, Michigan. That was a national emergency?