This paper considers how electoral competition affects voters turnout and candidate choice. We do so via an instrumental-variable (IV) bivariate probit with selection which jointly estimates both processes. Our analysis controls for individual and election characteristics, campaigning, and election day weather. We focus on the effects of negative advertising (tone) and overall spending (intensity) on several aspects of voter behavior, including abstentions. Our findings: tone increases turnout of Independents only, and can strengthen partisanship among non-voters. Campaign intensity matters more than tone. Overall, there is evidence that Democrats, Independents and Republicans have different propensities to react to campaigning, which do not follow a straightforward pattern. We also show that failure to consider turnout in voter choices leads to erroneous conclusions.