Districts becoming more Republican and Democratic

Republican districts moved right in 2012 and Democratic districts moved left.

When the state legislatures were doing redistricting, they were counting on making safer districts. They appear to have done their job too well. Districts that were R+20 or greater in 2008 moved on average 1.6 PVI points to the right. Overall, 74% of the 2008 R+20 or greater districts moved more Republican and 26% moved more Democratic.

For the most part the movement left in Democratic leaning districts and right in Republican leaning districts lessened as the districts moved closer to the middle. This is the exact opposite of what the legislatures would want. If you're Democrats you want D+2 districts moving 3 points left and don't care what happens in D+20 districts.

The popular meme is that the country is becoming more polarized and this seems to confirm that. Either voters are conforming more to their neighbors or Republicans are moving to Republican areas and vice-versa.