John Sides calls the idea that negative ads are effective a "zombie idea" unsupported by research in political science:
[W]e haven’t remotely arrived at a place where "research" suggests that negative ads "work." I’m not asking that reporters or commentators or foundations say that it "never works." I don’t think the literature suggests that either. I’m just asking for some engagement with this research. I think good reporting demands it.
Phil Arena counters:
If we assumed that 1) negative advertising typically turns voters off, 2) yet typically increases the relative share of the vote that will be garnered by the candidate running the negative ads, and 3) candidates have reasons to want to avoid the former effect when they already believe they are likely to win, we would expect to find that negative advertising does not work when we compared the vote shares of candidates who go negative to those who do not…I don't know that, in this particular case, we've got much ground to stand on when we admonish journalists for failing to engage with the relevant poli sci literature. Because I'm just not sure it tells us much yet.