Well if he had any guts he could just push to legalize drugs and then the cartels lose too.
That's actually brilliant in an odd way.
Legalize drugs and open up clinical dispensaries.
Spend 20~? Billion on education and addiction treatment.
Watch healthcare, addiction, crime and homelessness plummet.
Watch all drug use decrease and the cartels either forced to go legal or lose one of the largest markets.
You forgot the biggie: government makes money off the excise tax they place on the newly legalized drugs. Normally I'm against taxes but I think I would be ok with an excise tax on recreational drugs as long as the profits are used to fund the clinics and any related medical bills. Then the addicts are essentially funding their own treatment when they overdose and since it's in a clinic there are trained medical professionals to render treatment immediately.
But then he won't need the wall! So, yeah, it's a win for the drug cartels.