Who's responsible for increasing political polarization? Andrew Gelman suggests that one of the "cleanest pieces of evidence" is public attitudes toward abortion. If you look at the polling data, what you see is that attitudes between Democrats and Republicans start to diverge markedly around 1990. If you dig a little deeper, you find that the change is almost entirely among whites. If you dig a little deeper among whites, you get this:
The biggest change in party polarization on abortion appears among those with mid to high incomes; those with college degrees; and those who are heavily tuned into politics. Among the fabled blue-collar whites, party ID doesn't really predict attitudes on abortion very well at all.
Gelman avoids drawing any broad conclusions from this, and so will I. But it's interesting, especially since we've seen lots of evidence like this before. It's elites who have largely turned our major parties into polarized war zones, not the heartland.