Tanks serve no purpose, unless they are backed by infantry.  Tanks break things, and destroy structures.  They are overwhelmed by masses of people armed with marginally flammable materials.  The army of illegal criminal aliens are not structures, but mass of human beings.    Unless the army of illegal criminals is bringing armored vehicles with them, tanks won't offer much to augment defense unless they have beehive rounds to fire. I predict this army of illegal criminal aliens will be fought and defeated well in side the Mexican boarder - 50-100 miles, primarily by air assets, then on the ground by special ops if necessary.