I'm not sure I agree with Brett here. It really seems like a caste society is more rigid than what we have and what we have had here in the US. For example, my maternal grandfather was born on a homestead in Northern Idaho to a family that was trying to make it farming, selling a few logs here and there, etc. He was born in 1911. He got a law degree and became a professor. It's hard to imagine that happening in a truly caste-based society.
Not arguing that we don't have inequality. Just saying that it's not as rigid as I think of when I hear "caste."
Now, bringing in Murray's new book, as Wente does, is interesting. We have seen things like the Marriage Project's study of families that seems to imply that Murray is right. It shows that stable marriages are becoming a thing of the middle (and up) classes. That might imply that there are coming to be real social differences that go along with class differences. However, I'm still not sure that these are deep enough and impereable enough to make us a caste society.