An Update on Political Polarization (through 2011) – Part III: The Presidential Square Wave

Below we plot the estimated positions of presidents between 1945 and 2011 along the liberal-conservative scale, which produces a pattern we call the “presidential square wave”. Because we use first dimension (ideological) Common Space DW-NOMINATE scores, presidential locations are directly comparable across time. However, because presidential estimates are based on a limited number of “presidential support” votes– roll calls on which the president clearly indicates his support or opposition to a particular (often contentious) measure, presidential ideal points are somewhat biased towards the ideological extremes (however, this effect is roughly constant for all presidents, so it is unlikely than any particular estimate would be affected more than others).

Our findings here echo those discussed in a prior post that Republicans have moved further to the right than Democrats to the left in the contemporary period. Indeed, as seen below, President Obama is the most moderate Democratic president since the end of World War II, while President George W. Bush was the most conservative president in the post-war era.

Note: We have updated this image after a number of readers suggested we make the reference line for 0.0 more easily distinguishable from the other horizontal gridlines. We have also expanded the y axis to make it symmetric around -0.8 and +0.8. The presidential coordinates and the substantive findings remain the same.

Click image to enlarge.

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