Fostering Costly Political Engagement with Moralized Messages: Evidence from a Digital Field Experiment in Austria

While parties remain central institutions of democratic politics, party activism has been declining. Amidst the rise of populist parties across Europe, how can mainstream parties mobilize their base to participate actively? This paper theorizes that political parties can mobilize their sympathizers into activism (e.g., donations, volunteering) through moral language that appeals to ethical values. Building on social and moral psychology, I argue that moralized messages can incite a sense of moral conviction around a shared cause, triggering action-oriented emotions that motivate like-minded citizens to donate their time or money. In particular, as some populist actors prominently undermine democracy, I argue that mainstream parties can engage their sympathizers by inciting them with a sense of moral commitment to democratic values like diversity and equal opportunity. To empirically assess this, I partner with an Austrian political party for a randomized field experiment with behavioral data. This improves upon existing research on moral conviction in political psychology, which has tended to rely on correlational evidence and self-reported data. The experiment was implemented on a sample of party members and sympathizers subscribed to the party's newsletter (N=19,656). Subscribers were randomly assigned to receive—as part of their regular newsletter feed—either emails using moral language, or emails using non-moral language, or no experimental messages at all (in a control group). Both treatment arms involved emails criticizing populist actors, defending the party’s stance on similar policy issues, and asking recipients to donate money and perform activism. However, they differed in that the moral messages emphasized fundamental democratic values such as freedom, fairness or inclusion, while the non-moral messages emphasized pragmatic values like efficiency, cost-effectiveness or feasibility. As outcomes, I track individual-level donations to the party, sign-ups to volunteer, and party membership applications, as recorded by the party. Using these outcomes, I show that subjects exposed to moral rhetoric become more engaged, increasing their value in a composite activism index by 200% relative to the control. The effect is driven by moral messages increasing donations for the party, a costly form of political engagement. In contrast, there is no evidence that non-moral emails mobilized participants in any way, even though such emails were opened at similar rates as moral messages. By evaluating moralized messages in a naturalistic experiment with real-world behavioral data, this paper shows that moral rhetoric constitutes a valuable mobilization tool for activism in times of democratic threat. Crucially, messages eliciting a sense of moral conviction can motivate politically interested citizens to engage in costly political action. In so doing, I contribute to scholarship on the psychological roots of activist political engagement, rhetorical moralization, and party strategies in response to the rise of populist competitors that challenge democratic norms.