A central question in the study of democratic polities is the extent to which elite opinion about policy shapes public opinion. Estimating the impact of elites on mass opinion is difficult because of endogeneity, omitted variables, and measurement error. This article proposes an identification strategy for estimating the causal effect of elite messages on public support for European integration employing changes in political institutions as instrumental variables. We find that more negative elite messages about European integration do indeed decrease public support for Europe. Our analysis suggests that OLS estimates are biased, underestimating the magnitude of the effect of elite messages by 50%. We also find no evidence that this effect varies for more politically aware individuals, and our estimates are inconsistent with a mainstreaming effect in which political awareness increases support for Europe in those settings in which elites have a favorable consensus on the benefits of integration.