The entire United States, not merely the schools you cited, is "post-Christian" now and is recognized as such internationally and viewed as a fertile missionary field, so much so that several countries are sending missionaries to the USA. I work in Fullerton, in Southern California, and there is a huge and growing presence of expatriot South Korean Christians there for that very purpose.
The African Churches ARE in fact deluging the USA with missionaries!
Read “Never Silent!” by Thad and Erilynne Barnum.