A fortuitous follow-up to last-night's post. NPR's Day to Day ran a piece on research that Bill Bishop and Robert Cushing of the Austin American-Statesman have been doing on changes in voter demographics. The whole article (registration required, or see Timothy Noah's re-digested version at Slate) is worth reading, but the gist is that for the past 30 years, American communities have been tilting increasingly either Democratic or Republican. Bishop asserts that this increase in "landslide counties" (60% or more majority for one of the two parties) is responsible for the increasingly polarized political climate:

American democracy is based on the continuous exchange of differing points of view. Today, most Americans live in communities that are becoming more politically homogenous and, in effect, diminishes dissenting views. And that grouping of like-minded people is feeding the nation's increasingly rancorous and partisan politics.

Bishop doesn't speculate why Americans are self-segregating along party lines, nor does he address how the large portion of Americans who refuse to participate in the political process (perhaps out of disgust over the polarized climate) fit into this picture. Still, this is food for thought.