Do negative campaign ads work?

Not really, so it would appear:

Take the “daisy ad.” Perhaps the most infamous negative presidential ad of all time didn’t appear to move either Lyndon B. Johnson’s or Barry Goldwater’s poll numbers. And don’t be fooled by accounts suggesting that a negative ad had some subtle effect on a race — “changed the narrative” or another similarly squishy phrase. Votes, not narratives, are what wins elections.