People vary in the extent to which they imbue an attitude with moral conviction; however, little is known about what makes an issue transform from a relatively non-moral preference to a moral conviction. In the context of the 2012 U.S. presidential election, we test if affect and beliefs (thoughts about harms and benefits) are antecedents or consequences of participants’ moral conviction about their candidate preferences, or are some combination of both. Using a longitudinal design in the run-up to the election, we find that, overall, affect is both an antecedent and consequence, and beliefs about harms and benefits are only consequences, of changes in moral conviction related to candidate preferences. The affect results were consistent across liberals, conservatives, and moderates; however, the role of beliefs showed some differences between ideologues (liberals and conservatives) and moderates.