Two Decades of Polarization in American State Legislatures

One of the most robust findings in American politics is the decades-long trends in the level of elite partisan polarization. Among the most consequential of these trends has been that of state legislators. Polarization among these officials has had significant ramifications for political representation, policy making, and the workings of the US federal system. In this paper, we update the analysis of Shor and McCarty (2011) with comprehensive data from 1996 to 2020 for the state legislatures of all fifty states. We extend the analysis of state legislative polarization back to 1977 for a select set of states. These updates reinforce our earlier findings about the pervasiveness of polarization and its links to national trends. The new data also highlight features of polarization that appear unique to the states. While the polarization US Congress has been characterized by an asymmetric pattern of GOP movement to the right, the predominant asymmetry in the states is one characterized by Democratic movement to the left. Additionally, we discuss the burgeoning literature on evaluating the causes of polarization using our measures as well that identifying its consequences.