Income Inequality and Electoral Theories of Polarization

Both the academic political science literature and the popular discourse are replete with narratives seeking to explain the concurrent rise of income inequality and legislative polarization over the past half century. We focus on a prominent subset of such accounts, which posit the faithful representation of polarizing constituencies as the key causal mechanism linking the two phenomena, and which we therefore refer to as “electoral theories of polarization.†We show, however, that constructing a coherent, causal electoral theory of polarization is substantially more complicated than the literature has appreciated. First, we enumerate the necessary ingredients, with special emphasis on the importance of accounting for electoral geography. Second, we develop a causal framework for assessing the effect of income on polarization via a particular electoral channel, and we propose a set of estimation strategies that researchers may tailor to their particular model of how legislative ideology and partisanship are (co)determined. Third, we apply our framework to evaluate how well a model of self-interested “pocketbook voting†can explain patterns of polarization on the economic dimension observed in the U.S. Senate from 1984 to 2018. We conclude that voters’ private benefit from redistribution is unlikely to be a mechanism linking inequality to polarization.