I know this won't happen, but...
... perhaps the time is coming to seal the US/Mexico border shut.
COMPLETELY shut.
No vehicles in or out, including commercial vehicles.
The only way to move humans or cargo between the United States and Mexico should be:
1. By air;
2. By sea;
(both of these means are far easier to monitor and control than a "rubber tire" border crossing point)
3. By rail. This would involve building a "gauntlet track", say, a half-mile long with gates on either end, walls on either side, and a sealed screen top. When a cut of cars needs to move from Mexico to the US side, it will be pulled into the gauntlet, then "gone over" with ICE agents, dogs, etc. and "cleaned out". Any illegals found would be offered "the open door" -- on the "Mexico end". Once "sanitized" the Mexico doors would be closed, the US doors opened, and the train would proceed into American territory.
Again, I know this won't happen.
But if I was runnin' things, that's what I'd do.
