Affective and social political polarization—a dislike of political opponents and a desire to avoid their company—are increasingly salient and pervasive features of politics in many Western democracies, particularly the United States. One contributor to these related phenomena may be increasing exposure to online political disagreements in which ordinary citizens criticize, and sometimes explicitly demean, opponents. This article presents two experimental studies that assessed whether U.S. partisans’ attitudes became more prejudiced in favor of the in-party after exposure to online partisan criticism. In the first study, we draw on an online convenience sample to establish that partisan criticism that derogates political opponents increases affective polarization. In the second, we replicate these findings with a quasi-representative sample and extend the pattern of findings to social polarization. We conclude that online partisan criticism likely has contributed to rising affective and social polarization in recent years between Democrats and Republicans in the United States, and perhaps between partisan and ideological group members in other developed democracies as well. We close by discussing the troubling implications of these findings in light of continuing attempts by autocratic regimes and other actors to influence democratic elections via false identities on social media.

The study of the “authoritarian personality” began in Europe with the rise of Hitler as an effort to understand why so many seemingly ordinary Germans (and others) were willing to lend their support to an obviously anti-democratic and racist leader. Research on authoritarianism continues in this vein today, although it is now used throughout the world to explain why many people oppose democratic institutions, support authoritarian leaders, and hold prejudiced attitudes. The study of authoritarianism is as popular as it is controversial, with scholars disagreeing over whether it is a personality characteristic or a set of attitudes, how it develops, whether it occurs only on the political right or on the left as well, and how it is best measured, among other debates. Even so, scholars generally agree on the characteristics associated with authoritarianism: those who exhibit authoritarianism tend to be high group identifiers, submissive to in-group authorities, traditional and conforming, and aggressive toward those who either defy accepted norms or are members of outgroups. As has been evident for decades, authoritarianism is closely associated with all manner of highly consequential social and political attitudes, including anti-Semitism, racism, xenophobia, and homophobia, opposition to civil liberties and rights, support for war, and, of course, support for leaders who govern in an authoritarian manner.