It had better be thousands, tens of thousands of troops, otherwise it is a joke..
Establish a buffer zone on the Mexican side of the border. Erect tents, provide water, and MREs. Put a barbed wire fence around the whole thing and tell them here you will be safe. The only door out is into Mexico. Per international norms Mexico is the receiving country and it is their responsibility to provide for these refugees. They don’t get to just pass them on.
>>It had better be thousands, tens of thousands of troops, otherwise it is a joke..<<
Not so, because just the appearance of the military patrolling the border will have an extremely chilling effect on would-be trespassers. Indeed I predict there will be a near complete stoppage of border crossings before the military even shows up there.
...and drones; lots of drones.