Aggregate Effects of Large-Scale Campaigns on Voter Turnout

To what extent do political campaigns mobilize voters? Despite the central role of campaigns in American politics and despite many experiments on campaigning, we know little about the aggregate effects of an entire campaign on voter participation. Drawing upon inside information from presidential campaigns and utilizing a geographic research design that exploits media markets spanning state boundaries, we estimate the aggregate effects of a large-scale campaign. We estimate that the 2012 presidential campaigns increased turnout in highly targeted states by 7–8 percentage points, on average, indicating that modern campaigns can significantly alter the size and composition of the voting population. Further evidence suggests that the predominant mechanism behind this effect is traditional ground campaigning, which has dramatically increased in scale in the last few presidential elections. Additionally, we find no evidence of diminishing marginal returns to ground campaigning, meaning that voter contacts, each likely exhibiting small individual effects, may aggregate to large effects over the course of a campaign.