Enough already. The Kleptocracy to the South and their entertaining collection of thugs and narcotics cartel barbarians have been shipping illicit substances (which I would suggest would be far less trouble if they were simply all legalized), illegal immigrants, and now violence north of the border as their nation melts down into another Somalia-like ungoverned swamp of random violence, tribalism, and criminal syndicates seething on our southern border.
The violence is kind of the kicker that pushes things over the line to where I'm willing to reluctantly consider the "something must be done" meme (a meme which, 95% of the time when uttered, means someone is trying to run a con job). And I dislike addressing a problem without offering a solution.
Not being up for a full-bore war to the south, I'd propose a mile-deep DMZ on US Territory (and yes, condemning that much land isn't going to be cheap) modeled on the Korean DMZ - complete with automated machine guns.
We get a huge nature preserve out of the deal, and a secure border. Mexico gets to continue its own path, whatever that is, but without the U.S. as a handy relief valve and source of easy criminal profits from the sale of illicit items on a violent black market. Mexico retains its sovereign status - a matter in some doubt if things continue down their present path.
I'd expect an initial body count...dropping off rather fiercely to levels below the current count of bodies in the SW deserts due to hypo and hyperthermia, dehydration, and ill treatment. I anticipate a reduction in violence on both sides of the border as drug mules become impractical to move product across the border. And I predict the launch of an immigrant laborer program not unlike that which existed in past eras - most likely with the opportunity to stay permanently after a period of good conduct.
Mexico is a land filled with wonderful people of much diversity and talent, a rich culture (more or less in spite of the various governing authorities there over the years), in a state of melt-down. I'm not thrilled about the need for some kind of solution, but securing the border forcefully seems the only way to halt the flow of violent insanity now engulfing Mexico from heading north short of staging a full-out invasion.