The US lost its national backbone with the completion of WWII. Since that time, we've been a country of wobblers and spineless jerks. If we were willing to do what it takes to rid ourselves of Mexico's spreading disease, we could. Reapers work well, as do Predators. Closing the borders and insuring that they stay closed work also. You need to keep forcing the issue, and you need to learn to treat the enemy like an enemy, not like an estranged family member. I'd deliver paraquat to the Mexican poppy fields and marijuana fields by drone. It works well to kill the plants, and at the same time makes the product less than desirable because it's carcinogenic. And that's just for starters. Spraying the people maintaining the fields with paraquat isn't a bad idea either.
"An unarmed man can only flee from evil, and evil is not overcome by fleeing from it.“