James Moody and Peter Mucha published a fascinating article recently on the polarization of the United States Senate. Given their findings (published in Network Science, 1:1, 119-121), senators are farther apart, and are more partisan than at any point since the early 1900s. To put it differently, there are more straight, party line votes than at any point during the past century, which means we see lots of Democrats voting against lots of Republicans on many, many issues. The research also shows, obviously, that there are fewer and fewer individual senators who are willing to maintain moderate positions across a host of issues. To access one chart, and to get a brief summary, go here.

This is fascinating on so many levels, at least for political nerds like me. Let’s walk through some of the possible causes and implications for this. Remember, in the original Constitution, U.S. Senators were selected by state legislatures. This motivated office-holders to seek the state’s interest, and it meant they were chosen by a group that had already been selected to serve in office. Wrapping all of this together, these conditions created different kinds of political concerns and different kinds of senators themselves. As of the Seventeenth Amendment (passed in 1917), U.S. Senators are now directly elected by the voting population. Of course, this has made those chosen more responsive to the people as opposed to the state and its interests. In some ways, we might expect that shift to lead to more moderate politicians because states are large, diverse, and put varying kinds of pressures on individual office holders. So, even if you are from North Dakota, where the livestock outnumber the people, you still have strong agricultural, environmental, religious, and cultural pressures that hit office holders from different directions, which should favor moderate politicians who are able to appeal to a variety of perspectives and interests. Clearly, this has not happened.

At the same time, one prevailing trend in American politics has been a move away from party-centered elections and toward candidate-centered contests that focus on image, personal fundraising, and narrow issue appeals, as opposed to a full embrace of a party platform. Again, one would assume, this should lead to more moderate politicians since they are elected based on factors that are not necessarily partisan or ideological, especially when there seems precious little a political party can do to punish someone. Clearly, this has not happened, at least according to the measures used in the article.

What we may be seeing is that our states have become more polarized, and these have yielded candidates who must reflect those relatively extreme electorates in order to win office. Think of the 2012 election as a shorthand bit of analysis for this possibility. Of the 50 states, only FIVE had elections where either candidate won by less than 5% of the vote in the state (CO, OH, VA, NC, FL), while only another FIVE (NV, IA, WI, PA, NH) were settled by less than 7.5% of the vote. Of all the states, then, only 20% of them were remotely competitive in the presidential general election.

Perhaps, then, our Senate is merely a reflection of our states, which have settled into pretty definable patterns of partisanship over the past several cycles. While nothing is permanent, and these cycles can be either short or long-lived, it is interesting to ponder.

I hope, also, this helps put to rest a common misconception that people have about our political parties. One of the simply uninformed complaints about our political system is that the parties are basically offering the same thing or that there is no difference between Republicans and Democrats. While it is probably true that there is a gap between our leadership class and the people, that cannot be used to obscure the reality that our parties are starkly different. They offer different philosophies of government and, to a degree, different philosophies of life. Put differently, we see hyper-partisanship in the U.S. Senate for a reason, because the parties themselves are quite polarized at the moment.

This stands in strong contrast to the 1930s-1980s, when we had large segments of conservatives and liberals in both parties. The South contributed a conservative wing to the Democrats, while the New England states provided a liberal influence on the G.O.P. Today, the parties have oriented themselves around both issues and ideology. This has not always been the case.