As the 112th Congress came to a close last year, bipartisanship made a rare showing. The U.S. inched its way up to the fiscal cliff, but Congress voted to yank the country back, with 85 House Republicans voting not to reinstate the Bush tax cuts for individuals who earn more than $400,000. It was a rare moment of bipartisanship, however begrudging, for a Congress that has steadily become more polarized in the past 30 years.
Using a statistical analysis of some 35 million individual campaign contributions from 1980 through 2012, we assembled Congress’ polarization ratings. Rather than base legislators’ ideology on how they vote, we instead infer ideology scores from the patterns of contributions made by their supporters. In deciding which candidates to support, the typical donor is strongly influenced by his ideological views. As a result, they give almost exclusively to like-minded candidates with similar voting records. The massive quantities of data on contribution records (with over $6 billion dollars contributed to federal elections during the 2012 election cycle alone) make for an exercise in big-data and politics.
When you put all the data together, Congress’ modern history of polarization looks something like this:
The huge gap between the parties is apparent. We may hope that senators and representatives reach across the aisle, but the aisle is now as wide as the Grand Canyon. (The last chart for the Senate and for the House shows the forecasted distribution of ideology for the 113th Congress.)
Both houses in the 113th Congress should be the most polarized in American history. A big burst of additional polarization is anticipated for the Senate. The change for the House is smaller, reflecting the minor changes in House partisan balance after the elections. Polarization stabilized somewhat following the 2006 and 2008 elections as the Democrats engaged centrist candidates to contest formerly Republican districts. But the arrival of the Tea Party in 2010 led to a burst of polarization in the ensuing Congress. The 2012 rush reflects Republicans being replaced by liberal Democrats.