- The legislative calendar has become so full that members spend all their time in DC either voting or caucusing with their parties; they don't have time to speak to each other any more.
- The House has become increasingly partisan (in part due to redistricting), and more House members are ending up in the Senate.
- The majority has increasingly "filled up the amendment tree," making it harder for minority members to have any influence on legislation.
- Minority members increasingly respond to this by filibustering.
She acknowledged attributes of the political environment outside DC that have changed over the past few decades, but her main focus was on institutional features. And that's certainly understandable -- that's the stuff that's been in front of her face for the past four decades. But I think that a lot of what she sees as causes of polarization are actually consequences. The real story has been going on outside the Capitol, affecting what sorts of people get sent there in the first place.
How has the larger political environment outside of the Beltway changed? I address this a bit in a new blog post at Pacific Standard. Note, for example, the histogram below, which shows the distribution of states by presidential vote in 1968 (red) and 2012 (blue).
As I say in the post,
Notice how the red distribution basically has one peak while the blue distribution has two? That’s a sign of polarization. Senators who strictly voted how their states wanted in 1968 would have behaved much more similarly to each other than those who voted their states in 2012.That's certainly not the only thing going on affecting the way members of Congress behave. Indeed, there's plenty of evidence that legislators are considerably more extreme than their states and districts, even though those states and districts have become more extreme in recent years. But generally, if you want to understand why a legislature has become more polarized, look to the forces that send members there in the first place, rather than the behavior that they exhibit once they arrive.