Are high-income voters Democrats or Republicans?

Paul Krugman now has a blog, in which he makes brief but frequent posts. Many, of course, are related to his new book, The Conscience of a Liberal.

Recently he's made several posts about income and voting, and how the media's Conventional Wisdom is that "rich people vote democratic". He's also talked about What's the Matter With Kansas, the thesis of which is that low-income voters (e.g. Kansas) have been voting Republican, against their economic best interests, for the sake of social issues. Krugman presents evidence from Larry Bartels that lower-class voters continue to vote Democratic, the real shift is that upper-class voters are more consistently Republican. The other big shift is that white males in the South have moved to the Republicans, in backlash against the Civil Rights Act.

In comments, I've noted that the CW is not without foundation: high-income *states* definitely do vote Democratic in presidential elections. This seems to directly contradict the data Krugman presents showing that high-income *voters* vote Republican.

Is it something to do with income inequality? Or maybe regional differences in turnout?

You can tell I'm not an economist because thinking about this makes my brain hurt. Any economists/poli sci peeps out there who can lead me through the maze?