The reason is actually fairly simple. Negative ads make voters disgusted with politics in general. They raise the target’s negative ratings, but usually at the expense of raising the ad buyer’s negatives as well. Endangered incumbents love negative ads specifically because high voter enthusiasm and high turnout usually favor the challenger, so the more people you keep at home on election day the better your chances at keeping your seat.
The numbers add up just like you would expect them to. The GOP, essentially the incumbent party across the board, faces a tidal wave realignment election that could rival 1994 if they do not find some way to stem the bleeding. Neither stupid nor squeamish about bare-knuckle politics, the GOP did exactly what the numbers say they should do.
Does it work? Read Michael’s post. Moderate voter observes politicians throwing mud, throws up his hands and (if he was a US citizen) probably stays home. This isn’t rocket science.