Below are graphs of the difference between the Republican and Democratic Party means on the first DW-NOMINATE dimension from the end of Reconstruction through the the 112th Congress. This difference in first dimension means is a good measure of the level of political polarization. By this measure polarization is now at a post-Reconstruction high in the House and Senate. We also show pary difference in second dimension means, which have converged over time as the importance of the second dimension has waned.
With few exceptions, roll call voting throughout American history has been simply structured. Only two dimensions are required to account for the great bulk of roll call voting. The primary dimension is the basic issue of the role of the government in the economy, in modern terms liberal-moderate-conservative. The second dimension picked up regional differences within the United States — first slavery, then bimetalism, and after 1937, Civil Rights for African-Americans. With the passage of the 1964 Civil Rights Act, the 1965 Voting Rights Act, and the 1968 Open Housing Act, this second dimension slowly declined in importance and is now almost totally absent. Race related issues – affirmative action, welfare, Medicaid, subsidized housing, etc. – are now questions of redistribution. Voting on race related issues now largely takes place along the liberal-conservative dimension and the old split in the Democratic Party between North and South has largely disappeared. Voting in Congress is now almost purely one-dimensional – a single dimension accounts for about 93 percent of roll call voting choices in the 112th House and Senate – and the two parties are increasingly polarized.
Polarization declined in both chambers from roughly the beginning of the 20th Century until World War II. It was then fairly stable until the late 1970s and has been increasing steadily over the past 25 years. Our (Poole and Rosenthal, 1997) original D-NOMINATE estimation ended with the 99th Congress. Interestingly, Congresses 100- 112, if anything, mark an acceleration of the trend (especially in the House). Note, however, that the acceleration is smooth and does not show a particular jump in polarization induced by the large Republican freshman class elected in 1994. Polarization in the House and Senate is now at the highest level since the end of Reconstruction.
It could well be that we are seeing the beginning of an important battle, one that could herald a new conflict over the proper place for governing a free people.
Even as we become more polarized economically, we could become more united around a more important question dealing with the proper role of government in our lives.
Here is the graph in question, which shows in stunning detail just how polarized we have become since 1980.
I think the key to getting ourselves out of this mess is exposed in this work. What it represents is that all the roll call votes of every Congress can be imaged on a graph with just two axes. Not too complicated at all.
It turns out that every roll call vote ever taken by the House and Senate can be described along a two axis graph.
The first dimension most easily follows economic liberal-conservative issues. The second dimension has typically been a little more open to interpretation. It first picked up differences between views on slavery and on civil rights, issues that cut across the liberal-conservative spectrum.
Over the last generation, the importance of the second dimension disappeared almost entirely. Almost every decision was economic at base.
The sides are now so far apart on so many things that it becomes easy to explain any vote – liberal or conservative. All anyone really needs to know if which party someone is in and they know how any vote will go.
For example, a House vote on Obamacare.
You can easily separate the two sides with a single vertical line; the split is simply along the economic liberal-conservative dimension.
Recent votes have started to reveal a second dimension rift, one that has been called an establishment vs. outsider voting pattern. I think it might more accurately be called an authoritarian vs. civil libertarian divide.
Here is the best example, from the vote in the House on the Amash amendment to restrict NSA spying:
The split is now almost entirely explained by a horizontal line, one that follows the second dimension of an authoritarian-civil libertarian divide.
We are starting to see a second dimension arises when dealing with NSA spying. Now we see liberals and conservatives join together to strengthen the power of authority at the same time we see liberals and conservatives join together to oppose it.
During the founding of America, there were liberals and conservatives on economic policy who came together to find the right role for governing along the authoritarian-civil libertarian (monarchy vs. democracy) axis.. Similarly, the Civil War saw another struggle to find the right place for governing not along purely economic lines but also along the authoritarian axis (state vs. Federal, for example)
The Depression-WW2 again saw us battling across this second dimension to find the proper role for government (fascism/Communism vs. liberal democracies) Now we might be entering another period where the second dimension becomes important.
Which side are you on?