Why not just say that if there was a drug war that the guys in power could just close their eyes and wish all the drugs would just go away. That's about as plausible as the simplistic scenario you just listed there. closing the borders would not make much of a dent in the supply. You do realize we have thousands of miles of border and coastline in this country, right? Have you ever looked at a map in your life before?
I have looked at maps.
I have traveled extensively throughout the world as part of the US military, and fought real wars.
Borders can be closed - However “Implausible” that seems to your civilian ass.
There are these things that may not have ever penetrated your drug hazed mind called Fences, Mines, Cameras, and Aircraft. Sonar does a pretty good job at sea. Radar is useful too.
You seem to think it would require a whole lot of people locking arms and playing “Red Rover” on a grand scale.
That isn’t how China (Ever see China on a map?) secures her borders.