From the Washington Post:

The growth of income inequality has tracked very closely with measures of political polarization, which has been gauged using the average difference between the liberal/conservative scores for Republican and Democratic members of the House.

“The proximity of these trends is uncanny,” according to a 2003 paper by researchers Nolan McCarty, Keith T. Poole and Howard Rosenthal. “Remarkably, the trends of economic inequality and elite political polarization have moved almost in tandem for the past half-century.”

Excellent commentary on this from Eric Byler at Coffee Party USA.