The debate over the effect of negative campaigns on vote turnout has not been settled. At present, studies demonstrating a mobilization effect seem to have the upper hand. However, neither side has offered a compelling theory of the causal mechanisms that connect negative campaigns and voter turnout. This paper identifies three mechanisms of voter motivation—republican duty, candidate threat, and perceived closeness of the election—and tests the influence of negative ads on each. The findings suggest that each works to plausibly translate exposure to negative advertisement into increased participation.