Trump just tell Mexico that the border is closed to all traffic by land. It will remain closed until you stop and hold the invaders. Only passport holders of US citizens will be allowed entry and that’s that.
It seems so uncomplicated and part of the oath taken by those who swear to enforce the Constitution.
If it is a group of illegal entrants it is an invasion. The only reason it is just a "potential" military invasion rather than a full-blown military invasion is because the illegal entrants are not wearing uniforms.
Given the ineffectiveness of our national politicians, it seems almost certain the morale of those Americans employed to protect our borders on a day-to-day basis is currently at an all-time low.
What will there be to do when they throw their hands up in the air and declare, "We have been overrun."?
History is full of examples and suggestions in this regard.