What if:
California split into two States. And what if the southern state had a preponderance of Hispanics. And what if some event caused them to demand separation from the USA. And what if a referendum resulted in which they voted overwhelmingly to either separate from the USA as a nation, or become a state of Mexico.
Ditto, Arizona and New Mexico.
Sound far fetched?? Don’t discount it. We live in strange times. Failure to control borders leads to unintended consequences. Remember Crimea!!
I do not see it. Look at Puerto Rico where the preference for independence has withered being in third place behind statehood and status quo. As in PR, why would Mexicans in the Southwest want to give up the welfare gravy train or those with legal status the opportunity to move to other parts to the US.