The ideological middle -- both in Congress and in the country at large -- is either dead or dying. This is not a new revelation.
But, rarely has the rising polarization in the country been explored as deeply as in new Pew Research Center data that seeks to explain not just the how but the why of our increasingly divided country. The entire report is very worth reading. One image from it, though, which documents where the average Democrat and average Republican have fallen on the ideological spectrum over the past two decades, really captures how much things have changed in recent years.
Here it is. (Just click the "animate data from 1994-2014" button.)
There are a few remarkable things in that animation. The first is how the "median Republican" moved to the ideological left from 1994-2004. The second is how in 2004, that movement stopped and immediately began to reverse itself. The third is how the median Democrat and Republican move rapidly toward their ideological poles starting in 2011.