With rampant polarization in current U.S. politics, it seems as though political partisans with opposing viewpoints are living in parallel realities. Indeed, prior research shows that people's impressions/attitudes toward political candidates are intertwined with their political affiliation. The current study investigated the relationship between political affiliation and intersubject neural synchrony of multivariate patterns of activity during naturalistic viewing of a presidential debate. Before the 2016 U.S. presidential election, 20 individuals varying in political affiliation underwent functional neuroimaging while watching the first debate between candidates Hillary Clinton and Donald Trump. Pairs of participants with more polarized political affiliations were higher in neural synchrony in a system of brain regions involved in self-referential processing when viewing the opposing candidate speak compared with that candidate's supporters regardless of which extreme of the political spectrum they occupied. Moreover, pairs of political partisans matching in the candidate they supported were higher in neural synchrony when watching the candidate they opposed compared with the one they both supported. These findings suggest that political groups' shared understanding may be driven more by perceptions of outgroups than of their own party/candidates.