What leads citizens to change their candidate preferences during televised debates? The present paper addresses this question with real-time response and panel survey data from respondents recruited in the run-up to the 2017 German national election. Probing the importance of party identity and performance perceptions formed during the debate, the analysis more closely examines several core determinants than has previously been done with real-time response data. The findings suggest, first, that only a strong or very strong party identity is an effective barrier to candidate preference change. Second, beyond party identity, ratings of candidates’ issue-specific statements on policy issues show a very strong effect, albeit regardless of personal issue importance. Third, this influence of candidate ratings does not seem to be mediated through changes in valence perceptions. Rather, viewers seem to form a general impression of the candidates which cannot be reduced to performance perceptions regarding policy issues.