I argue that candidates shape their issue agendas—the sets of related issues on which they focus—in part in response to the issue agendas of their opponents and that competitive campaigns stimulate candidates to respond to one another at higher rates. I test my theory of candidate interaction using weekly advertising data at the media market level from 146 statewide elections—54 gubernatorial and 92 U.S. Senate contests—from six election years and across all 50 states. I find that candidates systematically respond to one another's issue agendas and do so to a greater extent in competitive elections than in noncompetitive elections.
