That America has become more politically polarized in recent decades is a widely accepted notion, and though some observers dispute aspects of this trend, political scientists have found strong overall evidence to support it.
A 2009 study published in Presidential Studies Quarterly, “Opinion Formation, Polarization and Presidential Reelection,” uses American National Election Study data to examine trends in polarization since 1972, during the presidencies of Nixon, Carter, Reagan, Bush, Clinton and Bush. The researchers, based at the University of Wisconsin-Madison and Duke University, sought to better understand the relationship between political polarization and voters’ knowledge of an incumbent president. Ultimately, the scholars demonstrate how increased polarization and a president’s likely reelection may be related.
The study’s findings include:
- Voters inevitably learn more about a president over his time in office, and this can be measured by tracking the decline in uncertainty when survey respondents are asked to rate presidents. (Uncertainty is indicated by responses of “don’t know,” refusals to answer, or placements at 50 on a scale of zero to 100.)
- The presidents with the greatest levels of polarization — measured as the difference between approval among members of his own party and approval among members of the other party — were the ones who were reelected. The two with the least polarization, Jimmy Carter and George H.W. Bush, were not.
- The partisan gap has widened over time. “[The gap] increased an average of 1.7 points each election year, but … jumps substantially more in incumbent reelection years. The average partisan gap grows about 4 points for Democratic incumbents, while the partisan gap increases twice that amount for Republican incumbents.”
- The partisan gap is widening fastest among the voters who are most politically aware.
- Knowing more about a candidate is associated with greater polarization. “When a president sought reelection, we found that uncertainty in the incumbent candidate’s evaluations drops by 7.7 percentage points, [and] the partisan gap in these evaluations rises by 4-8 points.”
“The conventional view of U.S. two-party politics suggests that moderation is the key to winning elections,” the researchers conclude. “On first blush, George W. Bush appears to run against this expectation. Despite being a ‘divider’ rather than a ‘uniter,’ he managed not only to win reelection in 2004, but also to increase his vote share over 2000. Our analysis shows that this counterintuitive connection between polarization and incumbent reelection is not limited to Bush, but rather stems from learning patterns that operate within nearly every presidential administration.” Overall, the study notes, “The learning that takes place during governing tends to provide a president with an advantage in the reelection contest and contribute to partisan polarization during the first term in office.”