Here's how that looks in the House from 1982 -2013:
In the last three decades, the number of members in the middle in the House dropped from 344 (79 percent of the House) in 1982 to four (.9 percent of the House) in 2013. As the slide suggests, redistricting -- the decennial redrawing of the nation's congressional lines -- plays a major role in that decline. The last two nationwide redraws have largely been incumbent-protection efforts, making Republican districts more Republican and Democratic districts more Democratic. Self-sorting -- the growing tendency of people to live around like-minded people -- is also a major factor in the disappearance of the ideological middle in the House.
More intriguing -- and harder to explain -- is how the middle has dropped out of the Senate, which is not subject to redistricting. Because senators represent entire states, self-sorting should be less powerful. And yet, here's the Mehlman Vogel Castagnetti slide on the partisanship in the world's greatest deliberative body:
Well more than half of the Senate fit between the most liberal Republican and the most conservative Democrat in 1982. For the last two years, there has not been a single Republican with a more liberal voting record than any Democrat and not a single Democrat with a more conservative voting record than any Republican. Not one.
Taken together, there are four -- FOUR -- members of the ideological middle out of the 535 members of the House and Senate combined. That comes out to approximately .7 percent of the entire Congress. In 1982, by way of comparison, more than 75 percent of members of Congress were part of the ideological middle.
So, in the last 30 years, the middle has lost more than 99 percent of its membership in Congress. And when the middle is represented by less than 1 percent of the entire Congress, it's not an exaggeration to say the center is gone.