What would you do? Clearly the Border Patrol is at something of a disadvantage vis a vis the Mexican military.
Enforcing existing immigration laws and laws against employing illegal aliens won't stop these criminals. They're not coming to the USA to take real jobs. Their coming here to commit crimes.
We need walls along our borders and we need the military on those walls.
Theoretically, they would be controlling any and all point of entry into the US, including every mile of shoreline, every international airport, every sea port, every train and bus station where people are arriving from either Canada or Mexico.
Is there some common identifying, readily visible mark that all citizens have that would make it possible for the Army to just look at you and figure out whether you're a citizen or an alien?
Can they figure out on sight that I am a naturalized citizen in spite of my obvious Hispanic looks? Will they be able to differentiate between an American of mexican descent from El Paso, and a well-dressed border crasher from Mexico DF?