Michael Barone: Mexicans might stop coming.
Even if conditions in the US do continue to deteriorate I think Mexicans and South Americans will continue to stroll across the border, probably settling in areas that have been allowed to become majority Hispanic.
Is a crackup of the US in the cards? I don't know. Quebec still hasn't left Canada after all these years. Maybe in addition to "a geographical line, coinciding with a marked principle", conditions simply have to be dire enough before people get up off the couch and break out the torches and pitchforks. I think things could be quite dire though without any crackup happening, so long as the centralized government of a country is sufficiently powerful and invasive. It seems like a good deal of personal space would be needed to carry off a good civil war, which is not the case where the government can read your emails, texts, and bank statements, where government intrusion is easy (for the rulers), arbitrary, and devastating, and where the legions of government employees and dependents outnumber freemen. So maybe people living within the new US will simply continue to "secede from each other" into ethnic enclaves, all dependent upon/oppressed by the government -- as will be necessary by the way (once all sense of civic society and the values of free people doing good themselves and managing their own affairs is finally squelched) in order to hold the whole miserable thing together.
Mexican sugar skulls.