COLUMBIA, South Carolina (CNN) -- Tonight's debate can truly be called the "Clash in Columbia."

Compared to the first GOP presidential debate in California, tonight's face-off is getting nasty.

The gloves are off between the candidates as they question their rivals' stances on crucial issues.

Just moments ago, John McCain fired a shot at Mitt Romney over his change of position on abortion. It was just the latest of a number of swipes the candidates have been taking at each other.