POLITICO's James Hohmann reports from Florence, S.C.:

Rick Santorum laced into Mitt Romney on Sunday for an ad being run by an independent super PAC that accuses him of supporting legislation to let convicted felons vote.

“I believe in running a campaign that’s honest, that has real integrity,” the former Pennsylvania senator told more than 100 voters at a restaurant here in the heart of the Pee Dee region. “As you know Gov. Romney and Congressman Paul, for now three states, have been running a pretty hard, negative campaign – which I think tells you a little bit about their ability to appeal to people’s better sides.”

“If you do it legitimately, that’s fine…but repeatedly I think Congressman Gingrich has made the comment …that Gov. Romney has not been accurate in what his assessment is,” he added.

Then he cited an ad that the pro-Romney PAC Restore our Future began airing in Florida last Thursday.

“I’ve just run into this with Gov. Romney’s super PAC today,” Santorum said Sunday. “He’s got an ad out that says that I voted to let felons vote. Now it’s very interesting. I did vote in the United States Senate that someone who is a felon, who served their time, who got out of jail, who has served their parole and probation and after all that sentencing then they could go out and apply to have their voting rights renewed – which, by the way, is the exact law that’s in South Carolina.”

“Now Gov. Romney’s taken that and said Rick Santorum’s for felons voting, but that is a lie!”

“I think there’s only two states that don’t allow that. So to go out and mislead the people of South Carolina as to what our record is on this is just: Yuck!”

“Why would we? I expect that from Barack Obama. I don’t expect that from a Republican running for president.”

The crowd applauded loudly.