What Has Made Congress More Polarized?

By Sean Trende - May 11, 2012

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If you’ve been skimming this, now’s the time to stop doing so, as I’m about to stop speaking “geek.” There are three important limitations to the program. First, you are probably wondering: “Is -1 liberal or is -1 conservative?” The answer is “DW-NOMINATE doesn’t tell you.” It simply tells you how the legislators should be rank-ordered, relative to each other, and how far apart they are from each other in terms of ideology. We have to fill in the “conservative” and “liberal” labels based upon our real-world understandings of the legislators.

This isn’t a problem today, as we know that Bernie Sanders is a liberal and Tom Coburn is a conservative. Identifying the poles is therefore easy. But what about in the 1880s? What do “conservative” and “liberal” mean in that context? As discussed later, it is difficult to say.

Second, you are probably thinking: “But do we really need to look at all roll call votes? I don’t care how someone votes on the motion to proceed to the highway bill.” This is a more serious objection. NOMINATE absolutely weights votes on renaming post offices the same as the vote on the 2010 health care bill. You can see why this type of completeness might be important for political scientists hoping to divine granular distinctions between legislators, but might not be useful for purposes of general punditry.

In fact, this “completeness” might make things look more polarized than they really are. Ever since the mid-1970s, votes in the House for the “rule” and against motions to table or to recommit on bills have been more or less taken for granted as a matter of party loyalty if a member wants to progress in the House. It really is a big deal when a member casts a vote against the party on these. By including all of these votes, which are frequently party line votes even if the final vote is not, DW-NOMINATE can tend to make it look like liberals and moderates (or conservatives and moderates) within a party agree on more than they really do. This also goes to another problematic assumption behind DW-NOMINATE, which is that legislators cast “sincere” votes, e.g. they vote purely with regard to ideology and not with respect to other things, like logrolling, party loyalty, or cornhusker kickbacks.

The third, and most important, limitation is this: a score of -.5 means is that a member is quite liberal but only (a) relative to other people voting in that particular Congress and (b) relative to the issue agenda of that Congress. The scores have no absolute, fixed meaning.

This can have important implications. Consider the following example: Thirty-one Southern Democrats served in both the 71st Congress (1929-30) and the 76th (1939-40). Their median score in the 71st Congress was -.165. In the 76th the median was -.085. All of them except three saw their scores migrate “rightward” during this time period. One legislator, Fritz Lanham of Texas, who represented Fort Worth and some surrounding counties from 1919 to 1947, swung from negative .139 to positive .114. In other words he went from voting mostly with Democrats to voting mostly with Republicans (at least on economic issues; for reasons beyond the scope of this article, DW-NOMINATE effectively filters out racial issues in this time period)!

The explanation most would immediately reach for here is that the Southern Democrats became more conservative in response to Franklin Roosevelt. This is possible. But it is also possible -- and consistent with the historical record -- that they didn’t shift at all. Instead, we should consider that the House was populated with many more relatively liberal members from 1929 to 1939, and that the issue agenda changed from a conservative Republican one, which the Southern Democrats opposed, to a progressive Democratic one, which the Southern Democrats also opposed. Going from mostly opposing conservative Republican legislation to mostly opposing the legislation put forward by their progressive brethren would create an illusion of movement on the part of the Southern Democrats in terms of their absolute conservatism, when in reality they stayed the same. DW-NOMINATE simply gives us no particularly useful tools for discriminating between these competing explanations.

This brings us Mann and Ornstein’s claims, which I think we can now dispense with rather quickly given this understanding of what DW-NOMINATE actually does. One simply cannot say that Republicans are the most conservative they’ve been since the 1880s, because the DW-NOMINATE scores are created without any fixed meaning. A legislator with a score of .2 in 1880 could actually be quite a bit more conservative, based upon our current understanding of “conservative,” than one who received a score of .7 in 2010. Put differently, a legislator with a score of .2 in 1880 would almost certainly never have voted for Medicaid; a similarly situated legislator today would almost certainly vote to renew it.

In fact, the historical record suggests that while there are some similarities between the basic Republican platform in 1880 and today, on other issues such as free trade, the differences are quite radical (and the Republican position on free trade today would have been considered “liberal” in the 1880s). In fact, it’s debatable whether Republicans should even be assigned the conservative pole in the 1880s, or that the Democrats should be assigned the liberal pole (which would also make the current Democratic caucus the most liberal one in history as well), given the strength of laissez-faire “Bourbon Democrats” in the Democratic Party during this time and the Republican Party’s position on internal improvements and spending on things like education.

For the same reason, while the DW-NOMINATE data can show that the current Congress is the most polarized in history (since that is a relative measurement), they cannot really show us who is to blame for that polarization. Without any lodestone to hold the “center” steady, we can’t tell who has moved the farthest away from that “center.” And because we have a pretty good sense that the center shifts from Congress to Congress, especially when control of that body changes hands, it becomes almost impossible to make meaningful comparisons between even two Congresses, let alone over the course of multiple decades.

Again, to illustrate this point, DW-NOMINATE suggests that Congress became much less polarized in the 1920s and 30s, which is probably true.  But it suggests that both parties moved toward the center (and that both Northern and Southern Democrats, on average moved toward the center).  There simply isn't any support for the idea that the Democrats in the 1936 Congress were, on average, more conservative than Democrats in the 1926 Congress, at least in the sense that contemporary pundits use the term.  But as the agenda moved leftward, the rise of the Conservative Coalition has the effect of pulling both parties toward the center, even though, overall, both were probably becoming more liberal.

DW-NOMINATE remains a powerful tool, especially if you keep its limitations in mind and are looking at discrete Congresses (or really are interested purely in polarization). It even sheds interesting light on realignment theory. But it really doesn’t do any of the things the popular press is claiming it does, at least not particularly well. 

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Sean Trende is senior elections analyst for RealClearPolitics. He is a co-author of the 2014 Almanac of American Politics and author of The Lost Majority. He can be reached at Follow him on Twitter @SeanTrende.

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