On Demographic Change and Competitive Equilibrium in American Politics

In their seminal analysis of American elections, Stokes and Iversen (1962) demonstrated that each party’s share of the vote never strays very far from a competitive equilibrium. However, it is difficult to envision how this equilibrium will maintain amid changing demographics. The Republican leaning white proportion of the electorate is shrinking while the Democratic leaning Latino and Asian proportion is rapidly growing. These demographic changes threaten to tip the partisan balance in favor of the Democrats. Can the competitive equilibrium hold amid changing demographics? I answer this question in three steps. First, I analyze presidential election returns since the end of the Civil War. I confirm the presence of a competitive equilibrium. I then use a set of simulations to establish that demographic changes will tip the partisan balance in favor of the Democrats. I then assess how much the Republican Party will have to increase its level of support among whites and/or other groups to remain competitive. I find that relatively modest changes in white and/or Latino and Asian voting behavior will be sufficient to give the Republican Party an even chance of winning well into the future.