Visualizing Polarization in Congress

I've written a bit about polarization in Congress.  Every semester, as I teach my students about the nature of partisanship, I try to give them a visual sense of how the membership has changed over time.  Most often, I rely upon the work of Keith Poole, who has pioneered the study of congressional partisanship by creating a methodology that allows for the comparison of the membership over time.  DW-NOMINATE scores give individual members a place along a liberal / conservative continuum based upon their voting behavior.  By comparing individual members with their partisan colleagues, one is able to gauge each party's internal cohesion.  By comparing individuals with members of the opposite party, one can see how much polarization exists between Republicans and Democrats.

When one takes this data across all Congresses, one gets the amazing short video above.  As one plays through the 112 Congresses that we've had, one sees how polarized the current era has become.  Both the Democrats and Republicans have become more internally cohesive and more distant from each other.  Fewer and fewer members find themselves crossing party lines, making the passage of legislation that is broadly accepted across the ideological spectrum more difficult.

Check out Poole's site for more visualization of this dynamic.