Actually, probably in the millions.
I expect that the approach will evolve fairly quickly into massive refugee camps, and given the widespread destruction and poverty and collapse of central authority, that eventually a significant percentage of the population will end up in the US. Obama administration and congress will authorize refugee resettlement in the US in large numbers.
Camp of the Saints...a book written in the 1970’s foretold all of this. If he brings them here...I am ready to riot...in the streets...