Disagreements over whether polarization exists in the mass public have confounded two separate types of polarization. When social polarization is separated from issue position polarization, both sides of the polarization debate can be simultaneously correct. Social polarization, characterized by increased levels of partisan bias, activism, and anger, is increasing, driven by partisan identity and political identity alignment, and does not require the same magnitude of issue position polarization. The partisan-ideological sorting that has occurred in recent decades has caused the nation as a whole to hold more aligned political identities, which has strengthened partisan identity and the activism, bias, and anger that result from strong identities, even though issue positions have not undergone the same degree of polarization. The result is a nation that agrees on many things but is bitterly divided nonetheless. An examination of ANES data finds strong support for these hypotheses.

P arty identification is central to the study of American political behavior, yet there remains disagreement over whether it is largely instrumental or expressive in nature. We draw on social identity theory to develop the expressive model and conduct four studies to compare it to an instrumental explanation of campaign involvement. We find strong support for the expressive model: a multi-item partisan identity scale better accounts for campaign activity than a strong stance on subjectively important policy issues, the strength of ideological self-placement, or a measure of ideological identity. A series of experiments underscore the power of partisan identity to generate action-oriented emotions that drive campaign activity. Strongly identified partisans feel angrier than weaker partisans when threatened with electoral loss and more positive when reassured of victory. In contrast, those who hold a strong and ideologically consistent position on issues are no more aroused emotionally than others by party threats or reassurances. In addition, threat and reassurance to the party's status arouse greater anger and enthusiasm among partisans than does a threatened loss or victory on central policy issues. Our findings underscore the power of an expressive partisan identity to drive campaign involvement and generate strong emotional reactions to ongoing campaign events.

A poisonous cocktail of othering, aversion, and moralization poses a threat to democracy

The distinction between a person’s ideological identity and their issue positions has come more clearly into focus in recent research. Scholars have pointed out a significant difference between identity-based and issue-based ideology in the American electorate. However, the affective and social effects of these separate elements of ideology have not been sufficiently explored. Drawing on a national sample collected by SSI and data from the 2016 ANES, this article finds that the identity-based elements of ideology are capable of driving heightened levels of affective polarization against outgroup ideologues, even at low levels of policy attitude extremity or constraint. These findings demonstrate how Americans can use ideological terms to disparage political opponents without necessarily holding constrained sets of policy attitudes.

"Social sorting" is a concept used by Mason (2016) to explain the process by which individuals' social identities grow increasingly aligned with a partisan identity, reducing social cross-pressures on political behavior. Roccas and Brewer (2002) have found that individuals who feel fewer cross-pressures more strongly identify with their ingroups and are less tolerant of outgroups. Accordingly, we create "objective" and "subjective" measures of social sorting to help identify the mechanism by which individual partisans connect social sorting to partisanship in the CCES and a nonprobability Internet sample. As racial, religious, and ideological identities have cumulatively moved into greater alignment with Democratic and Republican identities in recent decades, American partisans have grown increasingly identified with their parties due to the psychological effects of identity alignment captured in objective and subjective sorting mechanisms. However, we find that this effect is more powerful among Republicans than among Democrats, due to the general social homogeneity of the Republican party. Contrary to the assessments of modern political punditry, Republicans are more susceptible to identity-based politics.