With just one day left before the primary in South Carolina, the mud-slinging has reached new lows.

The GOP presidential candidates and their super PACs are sparing no expense in their attacks on each other -- and the media is joining in as well.

The latest attack comes from Newt Gingrich's ex-wife, Marianne, who told ABC News that her former husband had wanted an "open marriage."

"And I just stared at him and he said, 'Callista doesn't care what I do,'" Marianne Gingrich recalled. "He wanted an open marriage and I refused."

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"If he's running for president, he has answers to give," she said.

Meanwhile, the former House speaker has denied the story, and he's trying to change the subject, lashing out against former Massachusetts Gov. Mitt Romney's robo calls.

"I fully expect the Romney camp campaign to be unendingly dirty and dishonest," Newt Gingrich said.

Former Pennsylvania Sen. Rick Santorum is also blasting Romney.

"The establishment is once again telling us to fall in line and vote for their backroom, hand-picked moderate candidate," Santorum said.

Spending on political ads now tops $12 million in South Carolina. The figure is record-setting compared to 2008 when $13 million was spent. But that was for heavily contested primaries for both parties.

The intensity of the ad spending and political attacks reflects the do-or-die nature of this state's race. Many believe a big win for Romney here will solidify his nomination.

The big spending also reflects the emergence of the super-PACs. Each of the Republicans has at least one running ads on his behalf.

In total, presidential campaign ads for this primary have run 25,000 times across South Carolina media markets.