Simply, Mexico is in a guerrilla war and the majority (54%, in a recent Reforma poll) of the population thinks the narco-guerrillas are winning.
The only existential threat the US faces in the near term, is from global guerrillas in Mexico and not the Middle East. A breakdown there could result in massive population movements, refugee centers, and the spread of guerrilla warfare into US border states.
Emphasis added. Odd how we’re hearing little about this in the States. Mexico is also a major exporter of oil to the US. This could get seriously crazy.