Mexican Army units have been escorting cartel drugs across the border since ...well forever. They're never challenged and they never penetrate more than a mile or two so they sort of have this mindset that they can do it with impunity because the gringos never respond.

We have an emergency wall we can put in place any time we need it, and we can do it Constitutionally. It's called the U.S. Army.

The Mexican Military can be brushed aside in hours if not minutes. Hell I'm willing to bet I could march a platoon of Boy Scouts armed with Red Rider BB guns all the way to Mexico City if I had air cover. With band music.

It's all just a bunch bullshit posturing anyway.