Mobilization and Backlash: Asymmetric Updating in Response to Campaign Ads

Applying a media market boundary approach to individual survey data, I show that political advertising on television increases the probability that viewers who identify with a party will espouse its positions, prefer its candidates, and turn out to vote. This is true no matter which party sponsored the ad, suggesting that an ad consolidates and motivates the sponsor's partisans while simultaneously engendering a countervailing consolidation and mobilization among supporters of the other party. My results are consistent with agents who judge a source's quality by their priors and highlight the importance of targeting supporters.