The tendency for people to rate attitude-confirming information more positively than attitude-disconfirming information (biased assimilation) was studied in a naturalistic context. Participants watched and evaluated the first 1996 Presidential Debate between Bill Clinton and Bob Dole. Regression analyses revealed that predebate attitudes but not expectations predicted postdebate argument evaluations and perceived attitude change. Participants evaluated the arguments that confirmed their predebate attitudes as being stronger than the arguments that disconfirmed their predebate attitudes, and they perceived their postdebate attitudes to have become more extreme than their predebate attitudes. Self-reported affective responses mediated the association between predebate attitudes and postdebate argument evaluations. The role of affect in information-processing theories and the significance of the findings for sociopolitical debates are discussed.