Willie Horton I would guess, he was talking of 1988.
That was not even a Bush ad. It was made by an independent organization.
It was extremely effective...(not just the ad, Bush mentioned Horton in speeches IIRC)...both in driving White suburban swing voters to the Reps, and in alienating any Black with any sort of selfrespect from the Republican party for years to come.
The ultimate irony for Dukakis was that nothing (not even Willie Horton) caused the blacks didn't turn out for him at all anyways.
As for the historical impact, Patrick1 is quite correct that people today who weren't alive or functioning in 1988 frankly just don't realize how bad crime was in the inner cities then. The ad was so bloody effective because it emphasized something that was factually accurate with the subtext (racial that it was) that people of that time related with.
Law and order was a huge issue in that day. In fact, I think it's probably the key issue that kept those inner suburbs from trending Democrat in the 1980s when the Republican party moved right on other social issues.