How do voters make up their minds when voting on a citizens’ initiative? Motivated reasoning theory makes a strong case for a partisan bias in the way citizens process information, but empirical evidence is mixed. We offer a more systematic test of the “party over policy” argument by integrating prior attitudes into the analysis of how voters respond to cues and policy information. Results of a survey experiment with pre-post measures of vote intentions on a California citizen initiative on online sports betting in 2022 provide support for partisan motivated reasoning. Regardless of the direction of policy information, voters who change their minds tend to follow the cue of their preferred party, even when the cue contradicts their initial vote intention. These results have important normative and practical implications.