Scholars have shown that voters are constrained by party identity in their reactions to negative attacks sponsored by in-group candidates. If party cues are no longer a reliable source for evaluating ad content, how do voters interpret and respond to negative advertising? The present research compares viewer responses to negative political advertising in one-party and two-party contests. Findings support a theory of "unconstrained backlash" in which negativity in both types of contests cause similar decreases in evaluations of the sponsor candidate, but the lack of constraints on party identity cause voters to cast harsher punishments upon ad sponsors in one-party contests.