Sounds like the background of my second novel.
(Art.) What if the worst happens and we go from 10-12 million illegals in the United States to 25-40 million packed into the southwestern United States in a relatively short period of time? Demographics are destiny.....
The author's behind the curve: we're already there with those numbers, or rather have been. It's like nailing Jell-O to a wall even to guess at a good number, because the Census Bureau, geeing to the nod of the PTB, has been drastically low-balling the number for years.
I would guess that the number of Mexican nationals in -country in illegal status (is there another?) is over 15,000,000 and that immigrated, amnestied, papered (legalized) immigrants, and first-generation "anchor babies" of same drive the total to around 30,000,000.
Recently there has been some recession of these big numbers as Mexicans bail for the old country as jobs dry up in the recession, so "your guess is as good as mine -- and maybe better".
WAG: a couple million "former illegals" with papers and voting rights are probably actually still illegal, slipping by with fraudulent documents and phony claims on citizenship. Not exactly a solid foundation for patriotism in the later generations.
Sounds like the background of my second novel.