I found this fascinating. Sometimes I come across a bit of information and instantly have a gut feeling that this is a key piece of information to understanding... something, I don't know what. Such was the case with this bit from CJR Campaign Desk on "Rural R's and Urban D's":

"In the 1980 presidential race, Democratic and Republican counties on average had about the same number of voters. By 2000, however, the average Democratic county had three times as many voters as the average Republican county. ...

In the country's most partisan counties -- those where one party wins by more than 20 percentage points -- the split is overwhelming. In 2000, the average landslide Democratic county was eight times larger than the average landslide Republican county. [By contrast] in 1980, the average landslide Republican county was more populous than the average partisan Democratic county."