Partisan polarization in the United States has increased the ideological uniformity of the Democratic and Republican parties, and therefore the usefulness of party identification as an indicator of candidates’ ideology. However, candidates – especially during primary elections – often attack their opponents for being insufficiently conservative or progressive, explicitly signaling to voters that they should put less faith in their stereotypes about the party’s ideology when evaluating candidates. To assess the effects of these ideological attacks, we conduct a Dynamic Process Tracing Environment experiment that simulates a primary election campaign. We find mixed evidence that participants, when exposed to an ideological attack ad, lower their ratings of the attacked candidate’s ideological extremity, overall favorability, qualification for office, and trustworthiness. However, we observe no differences between experimental conditions in terms of information search, suggesting that ideological attacks are generally accepted at face value and not independently verified by voters.