Why go negative? It works

For the first time in a presidential race, political action committees outside of a candidate's campaign can raise as much money as they want, spend as much as they want and support or attack any candidate they want. The so-called Super PACs are behind some of the nastier ads of the campaign season.

"South Carolina is known as a bare-knuckle state," said Karen Floyd, the former chairwoman of the state Republican Party. "I can tell you frankly, we see a lot of negative ads."

While voters often say the negative ads are a turn-off, research shows that they are effective.

"It's easier to get an attack ad and something that's memorable into a 15- or 30-second spot than it is to get out a positive message," said Dr. Robert Oldendick, a political science professor.

South Carolina, with its early primary and strongly conservative voter base, is a prime spot for this kind of advertising.

The candidates themselves say they don't like the negativity. But, since they're not paying for them, and they're working, a candidate is unlikely to ask a Super PAC to stop.

Brad Query, a registered Democrat, said the negativity hurts all the Republican candidates.

"I think it's the greatest thing they can possibly do," he said. "I think they've now proven that none of them are fit to run against President Obama."