Expect more negative political ad campaigns

Researchers declare that fear and guilt motivate better than hope.

"Smoking pot may not kill you, but it will kill your mother," says an ad from the Partnership for a Drug-Free America. In the first empirical work to examine both stated intentions and actual behavior, researchers argue that this sort of negative message – evoking both fear and guilt – is a far more effective deterrent to potentially harmful behavior than positive hopeful or feel-good messages.
"Making people feel good is less important than making people feel accountable when it comes to making wise decisions about self-protection," explain Kirsten A. Passyn (Salisbury University) and Mita Sujan (Tulane University) in the March 2006 issue of the Journal of Consumer Research...
... good intentions can be elicited by a variety of appeals. However, getting people to actually follow through on these intentions and change their behavior requires appeals combining fear and an emotion high in self-accountability, such as regret, guilt or challenge.

If this holds, then the popularity of negative ad campaigns is due to their effectiveness in motivating people to vote. Expect more in the future.