The idea of America as politically polarized--that there is an unbridgeable dividebetween right and left, red and blue states--has become a cliche. What commentators miss, however,is that increasing polarization in recent decades has been closely accompanied by fundamental socialand economic changes--most notably, a parallel rise in income inequality. In Polarized America,Nolan McCarty, Keith Poole, and Howard Rosenthal examine the relationships of polarization, wealthdisparity, immigration, and other forces, characterizing it as a dance of give and take and back andforth causality.Using NOMINATE (a quantitative procedure that, like interest group ratings, scorespoliticians on the basis of their roll call voting records) to measure polarization in Congress andpublic opinion, census data and Federal Election Commission finance records to measure polarizationamong the public, the authors find that polarization and income inequality fell in tandem from 1913to 1957 and rose together dramatically from 1977 on; they trace a parallel rise in immigrationbeginning in the 1970s. They show that Republicans have moved right, away from redistributivepolicies that would reduce income inequality. Immigration, meanwhile, has facilitated the move tothe right: non-citizens, a larger share of the population and disproportionately poor, cannot vote;thus there is less political pressure from the bottom for redistribution than there is from the topagainst it. In "the choreography of American politics" inequality feeds directly into politicalpolarization, and polarization in turn creates policies that further increase inequality.
Nolan McCarty is Professor of Politics and Public Affairs and Academic Dean of the Woodrow Wilson School of Public and International Affairs at Princeton University.