Hmmm...
Recent announcements of new stealthy aircraft (SR72, that Grumman drone).
Places like the Skunk Works and Area 51 that ordinary folks would be arrested (or worse) if they got too close. All this technology designed to secure the USA.
Yet we have all kinds of "drones" flying on the southern border (some across it, I'll reckon), some reported to be carrying explosives... and there's little that we DO about it?
One of the things Mr. Trump should do (presuming he has the luck to get re-elected in spite of The Party's underground and above-ground election apparatus) is to militarize the southern border.
ALL of it, from the Gulf to the Pacific, covering an area from the border itself to about 10-15 miles north.
If necessary, put that area under some reduced form of martial law and governance.
And then go in there with as many troops as necessary and clean it up.
Do you REALLY want the invasion stopped?
If so, how in heck do you think it's going to be done?