"Lower-income and less educated whites also have shifted substantially toward the Republican Party since 2008. The GOP has largely erased the wide lead Democrats had among white voters with family incomes less than $30,000." [0]

Although the graphs on [1] tell a slightly different story.

[0] - http://www.people-press.org/2012/08/23/a-closer-look-at-the-... [1] - http://www.npr.org/blogs/money/2012/09/26/161841771/how-inco...