Hmm, I wonder why those native-born Americans are moving elsewhere?
(My assumption here is that the hundreds of thousands of "foreign immigrants" are mostly illegals doing what illegals seem to be best at doing).
The problem is, the middle class is fleeing the cities and taking the tax base with them. The illegals coming into the cities are peasants without any skills or education. Taxes are skyrocketing due to the need for more social programs. In order for the schools to maintain their funding from the state, more taxes are needed.
To add more problems to the fire, when the middle class departs, wages will be reduced since immigrants work for peanuts. This is the start of the downwards spiral to a depression in metropolitan cities because housing and rent will go down since the qualified buyers disappears.