Partisan bias and hostility have increased substantially over the last few decades in the American electorate, and previous work shows that partisan strength and sorting help drive this trend. Drawing on insights from moral psychology, however, we posit that partisan moral convictions heighten affective polarization beyond the effects of partisanship, increasing partisan animosity and copartisan favoritism. Testing this theory using data from two national samples and novel measures of affective polarization in everyday life, we find that people who tend to moralize politics display more partisan bias, distance and hostility, irrespective of partisan strength. These results shed light on a different moral divide that separates the American public and raise key normative questions about moral conviction and electoral politics.

Studies provide mounting evidence that morally convicted attitudes elicit passionate and unyielding political responses. Questions remain, however, whether these effects occur because moral conviction is another strong, versus a distinctly moral dimension of attitude strength. Building on work in moral psychology and neuroscience, I argue that moral conviction stems from a distinctive mode of mental processing that is tied to automatic affective reactions. Testing this idea using a lab experiment designed to capture self‐reported moral conviction and physiological arousal, I find that conviction about political objects positively predicts arousal evoked by the objects, while attitude extremity and importance do not. These findings suggest that moral conviction items do tap into moral processing, helping to validate the conviction measure. They also illustrate the value of using physiological indicators to study politics, help explain why morally convicted attitudes trigger such fervent responses, and raise normative questions about political conflict and compromise.

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