Scholars disagree whether negative advertising demobilizes or stimulates the electorate. We use an experiment with over 10,200 eligible voters to evaluate the two leading hypotheses of negative political advertising. We extend the analysis to examine whether advertising differentially impacts the turnout of voter subpopulations depending on the advertisement's message. In the short term, we find no evidence that exposure to negative advertisements decreases turnout and little that suggests it increases turnout. Any effect appears to depend upon the message of the advertisement and the characteristics of the viewer. In the long term, we find little evidence that the information contained in the treatment groups’ advertisements is sufficient to systematically alter turnout.