From Many Divides, One? The Polarization and Nationalization of American State Party Platforms, 1918-2017

Abstract

Many contend that U.S. state parties are increasingly polarized and nationalized, meaning that they have adopted divergent positions matching their national counterparts’. Yet, the relationship between these trends and the mechanisms underpinning them remain open questions. We introduce a data set of 1,783 state party platforms between 1918 and 2017 to assess these dynamics. Applying tools from automated and manual content analysis, we find that innovative phrases increasingly debut in state (not national) platforms. We also document a dramatic divergence in the topics emphasized by Democrats and Republicans starting in the mid-1990s, just as congressional speech polarized. During this period, cross-state differences in issues decreased and regional/sectoral issues became less prominent, suggesting tight connections between polarization, nationalization, and state agendas. Overall, the evidence undercuts claims of top-down nationalization and is consistent with the view that polarization coincides with the development of an integrated network of activists spanning multiple levels of the polity.