Using this website
http://www.dimpledchad.info/result/, if one controls for education (so that you are comparing white voters across different income groups, but within the same educational group), one finds, as expected, that, for the most part, higher-income whites who have "some college" or "no college" (high school graduates) are much more Republican than lower-income whites within the same educational groups (Example: McCain got around 46% of whites in the "some college" category with annual incomes of under $30k, but about 56% with annual incomes of $30k-$50k, and over 60% with annual incomes of $50k or above).
However, the correlation doesn't work at the $75-$100k income level, even among white voters within the same region and the same educational level. McCain got 56% of the vote in at income level among white high school graduates, for example, but
65% of the vote among white high school graduates at the
lower income level of $50-$75k.
Why is this? My hypothesis is that the demographic "white high school graduates with incomes of $75-$100k a year" might be a good predictor of belonging to a unionized job or a small business owner who feels more financially stable, not struggling as much, and so less receptive to Tea Party's right-wing populist appeals.
Anyone else have any theories about this?