Remembering to Forget: A Note on the Duration of Campaign Advertising Effects

Exposure to an Obama campaign ad as part of an Internet survey conducted during the final weeks of the 2012 presidential race produced a substantial 2.8-point increase in intentions to vote for Obama. A post-election follow-up survey found an increase in reported votes for Obama that was only half as large, consistent with the notion that ad effects decay over time. However, a closer look at the pattern of decay indicates that the effect of ad exposure remained virtually constant among people who were undecided or predisposed to support Obama. The reduced aggregate effect was almost entirely attributable to Romney supporters who moved toward Obama in the immediate wake of ad exposure but returned to Romney by Election Day. This divergence is inconsistent with an interpretation of decay as reflecting simple forgetting. Rather, it suggests an active process of motivated reasoning in which short-term persuasive effects are gradually eroded or even reversed by counterarguing among people predisposed to resist them.