In the United States, the past quarter-century has been marked by two disturbing societal trends: increasing levels of both income inequality and political polarization. The rich are growing richer, and Democrats and Republicans are growing farther apart.
In 2006, a group of researchers led by Nolan McCarty, a professor of politics and public affairs at Princeton, presented evidence linking these two phenomena. They reported that "the average positions of Democratic and Republican legislators have diverged markedly since the mid-1970s," adding that "this turning point occurs almost exactly the same time that income inequality begins to grow after a long decline.”
So are we evolving into a nation of haves and have-nots, with one political party representing the interests of each? Research just published in The Journal of Politics, which examines voting records of the U.S. Senate, provides state-level evidence suggesting this dynamic is well under way.
"U.S. senators from states with high levels of income inequality are more polarized than other senators,” writes Louisiana State University political scientist James Garand, "primarily in response to state income inequality and greater constituency polarization that results from high income inequality.”
Examining individual political attitudes, state-level income inequality and the roll-call votes of U.S. senators, Garand comes up with some striking findings. Looking at data from the early 1970s to the mid-2000s, he finds that as income inequality rises in a particular state, the voting patterns of its senators shift.
"Increases in income inequality in senators’ home states move Republicans in a more conservative direction,” he reports, "resulting in a systematic increase in the difference in ideological positions for Republicans and non-Southern Democrats.”
Democrats, he adds, "respond to the same increases in state income inequality by moving moderately (but significantly) in the liberal direction.”
In summary, "High levels of income inequality generate high levels of political polarization in state electorates, and both income inequality and political polarization exhibit a strong influence on partisan polarization among U.S. senators.”
As Timothy Noah noted in his recent series in Slate, rising income inequality is a long-term trend that shows no sign of slowing. Garand’s analysis, like McCarty's, suggests the same can be said for the polarized nature of our politics.