CHARLESTON, S.C. - On his second day as a member of Team Romney, Sen. John McCain continued to assail former Sen. Rick Santorum for supporting so-called "pork barrel spending."

"Believe me, earmark spending is the gateway to corruption, and that was practiced when Republicans were in the majority," said McCain, R-Ariz. "Sen. Santorum and I have a strong disagreement, a strong disagreement that he believes that earmark and pork barrel projects were good for America.

"I think it's wrong for America and so does Sen. [Jim] DeMint and so does Sen. Lindsey Graham who have been staunch fighters against earmark and pork barrel spending," said McCain, evoking the names of two of South Carolina's senators. "And I know you're proud of that."

Earlier today, McCain made similar claims against Santorum on CNN's "Starting Point," referring to earmarking as a "gateway drug to corruption."

Romney, himself, has so far remained mostly out of the fray when it comes to outright attacks on Santorum, going only as far as to say that he is as much of a career politician as former House Speaker Newt Gingrich is.

In an informal press availability following the event, South Carolina Gov. Nikki Haley said that, unlike McCain, she felt no need to go after Romney's GOP rivals.

"I don't feel like I have to put any candidates down to make Gov. Romney look good," she said.

This was McCain's second day of campaigning with Romney. They met Haley in Charleston, S.C., this afternoon McCain stumped with Romney in New Hampshire earlier in the day.

This is Romney's eighth trip to South Carolina since announcing his candidacy in June, and he was welcomed by a crowd of about 400 people at the Charles Towne Landing historic site.

The ground game for the Romney campaign is already ramping up in the state, at least one of the four paid staffers from the Iowa team having already relocated to South Carolina.

Romney, McCain and Haley will hold another rally in Myrtle Beach, S.C., on Friday morning.