At least two theories have been offered that explain the rise of affective polarization. Some scholars, relying on social identity theory, argue that as the relevance of party identification increased, Americans became more likely to see their in-party in positive terms and the out-party in negative terms. Other scholars argue that affective polarization is a reaction to increasingly extreme political actors. This study seeks to arbitrate between these two theories of affective polarization through a survey experiment which asks respondents to rate candidates whose party (or lack thereof) and ideology (or lack thereof) is randomly assigned. In line with the policy-oriented view of affective polarization, respondents reacted far more strongly to ideology than party, especially if it was the ideology of the member of the out-party.