Presidential primary elections arguably represent the most dynamic campaigns in American politics. Television advertising is a key aspect of strategy that candidates can marshal throughout the campaign. We develop a methodology for measuring the impact of advertising in primary elections that accounts for endogeneity and apply it to the 2000 through 2016 elections. We find that advertisements—both positive and negative—improve the favorability and the vote share of the candidate running the ads. We find that negative advertising is more effective than positive advertising, but that only high polling candidates lose support when attacked.
