Partisans Without Constraint: Political Polarization and Trends in American Public Opinion

Political polarization is commonly measured using the variation of responses on an individual issue in the population: more variation corresponds to more people on the extremes and fewer in the middle. By this measure, research has shown that— despite many commentators ’ concerns about increased polarization in recent decades— Americans ’ attitudes have become no more variable over the past two or three decades. What seems to have changed is the level of partisanship of the electorate. We define a new measure of political polarization as increased correlations in issue attitudes and we distinguish between issue partisanship—the correlation of issue attitudes with party ID and liberal-conservative ideology—and issue alignment—the correlation between pairs of issues. Using the National Election Studies, we find issue alignment to have increased within and between issue domains, but by only a small amount (approximately 2 percentage points in correlation per decade). Issue partisanship has increased more than twice as fast, thus suggesting that increased partisanship is not due to higher ideological coherence. Rather, it is parties that are more polarized and therefore better at sorting individuals along ideological lines; the change in people’s attitudes corresponds more to a re-sorting of party labels among voters than to greater constraint on issue attitudes. We conclude suggesting that increased issue partisanship, in a context of persistently low issue constraint, might give greater voice to political extremists and single-issue advocates, and amplify dynamics of unequal representation.