The air wars are heating up in South Carolina, and Rick Santorum's newfound momentum has brought new criticism.

Ron Paul will hit Santorum with an aggressive new ad that accused the former senator of being a "corporate lobbyist and Washington politician" with a "record of betrayal":

The ad is Paul's first to focus on Santorum. The latest polling from WMUR/UNH shows Paul leading Santorum in new Hampshire, while both trail Mitt Romney. The latest polling from CNN/Time/ORC shows Paul in fourth place (12 percent) in South Carolina, trailing Romney (37 percent), Santorum (19 percent), and Newt Gingrich (18 percent).

The new ad will begin airing on Monday in South Carolina, Paul's campaign announced.