What up with red state blue state?

Jordan Ellenberg writes:

I learned from your book that Democrats doing better in richer counties and Republicans doing better in poorer counties did not imply that richer people were more likely to vote for Democrats and that in fact, the opposite is true. I do wonder, though, to what extent that’s changing with the current realignments, for example see here, which shows that the “rich districts vote Democratic” effect has certainly gotten stronger since your book came out. I wonder if, as Dems consolidate strength in both cities and suburbs while the GOP asserts dominance over rurall America, we will actuallly start to see the income/voting relationship switch signs at the individual level? Or are we still just seeing the familar scenario of high distric-level incomes driven by inequality while Dem voting patterns are driven by poorer residents? Do Democratic voters now tend to be rich, or do they just tend to live near the rich…?

My reply: I’m not sure, but see this article about red state blue state in 2012, and section 16 of this article about 2016. Also relevant for considering the long view is this article about the twentieth-century reversal.