Political Polarization in the U.S. Congress
If you think Washington D.C. is polarized, you’re right. Using Lewis, Poole, and Rosenthal’s NOMINATE data, I created the following animations showing how Congress has polarized from 1947 to 2023.
Below is a two-dimensional look at polarization over the same period. The x-axis, (Dim1) is the familiar left-right continuum; the y-axis, (Dim2), looks at salient issues of the day, like civil rights.
(You can click on any datapoint to see the member of Congress).
The technical definition of political polarization is intraparty homogeneity and interparty heterogeneity.
Intraparty homogeneity means, politically speaking, Democrats look like other Democrats and Republicans look like other Republicans. Interparty heterogeneity means Democrats and Republicans look nothing alike.
You can see this dynamic play out in the animated charts. From the 1950s to the 1980s, there was:
significant overlap between the parties (e.g., there were some conservative Democrats and liberal Republicans),
a healthy political middle, and
the median members of both parties weren’t that far apart. In the words of George Wallace, “there wasn’t a dime’s worth of difference” between Democrats and Republicans. (As usual, Wallace was wrong: there were differences between Democrats and Republicans. But, looking back on the “awful 80th,” that difference was far less pronounced then than it is now.
The animations show how a healthy stock of political moderates first became an endangered species and, ultimately, were driven to extinction. Today, Democrats and Republicans look like the Sharks and the Jets.
The next article will examine whether the American public has polarized as well. The one after that will explore the causes and consequences of political polarization.
