<p> How do social norms surrounding racial attitudes differ among white Democrats and Republicans? Do these norms differ from the prevailing “norm of equality,” and how do they affect civic discourse? Using a novel video-based discussion experiment, I show how co-partisan discussion among white Republicans (versus talking to a white Democrat) increases their racial resentment, as measured both in post-treatment surveys and the rhetoric subjects use during discussion. White Democrats do not significantly change their racial attitudes or rhetoric according to the partisan identity of their discussion partner. Among white Republicans, racially resentful language increases by more than 10% when discussing politics with a co-partisan compared to conversing with a white Democrat. This result is driven by the partisan identity of the discussion partner rather than the content of their speech. Even when a co-partisan takes a position on race-related policy that is counter-typical to their party (such as a Republican supporting affirmative action), white Republicans still use significantly more racially resentful language than when they talk to a Democrat, even one who “sounds like” a Republican on race-policy. Findings highlight polarization as a democratic social ill, suggesting consequences for American civic discourse around race. </p>