Romney was confident and relaxed campaigning Friday, traveling with his wife, Ann, and bringing reporters along on the campaign's charter flights for the first time this year.
Gingrich is still facing withering criticism from Texas Rep. Ron Paul and Minnesota Rep. Michele Bachmann.
Romney also hopes to slow Gingrich heading into New Hampshire, a must-win state for Romney, who was governor in next-door Massachusetts. Romney, who has led comfortably in New Hampshire, began airing a new ad there featuring his conversations with New Englanders concerned about the economy.
Romney already had set aside campaign money to step up his South Carolina effort, although the focus will probably remain on advertising, not additional campaign staff.
No doubt in the works for South Carolina is another Romney ad before the Jan. 21 primary, one featuring Haley.
Haley's ties with Romney run deep. She endorsed him in 2008 when she was in the Legislature. Romney returned the favor when she ran for governor in 2010.
"Neither South Carolina nor the nation can afford four more years of President Obama, and Mitt Romney is the right person to take him on and get America back on track," Haley, a rising GOP star, said after announcing her endorsement on Fox News Channel.
She later told The Associated Press that Romney "has led in making decisions," a point Romney stresses in suggesting his decades in business and term as governor qualify him most for the GOP nomination.
Romney has focused heavily on winning New Hampshire's primary on Jan. 10. But he has been spending time, too, in Iowa, where he finished a disappointing second to Arkansas' Mike Huckabee after spending $10 million on his 2008 Iowa campaign.
The candidates — except for Gingrich — were making final pitches to voters on Friday before people begin focusing on the holidays.
Bachmann and Texas Gov. Rick Perry were taking their argument that Gingrich isn't conservative enough to lead the party to Iowa voters on separate bus tours in the state's conservative but lightly populated northwest.
Although Gingrich was off the trail, his campaign drew unwanted attention after two New Hampshire Republicans alleged in complaints filed with state authorities that they had received illegal political telephone calls from the Gingrich operation.
New Hampshire law prevents political campaigns from using recorded political messages, or "robo-calls," to contact residents who are registered on a national do-not-call list.
Gingrich's campaign denied wrongdoing.
Associated Press writer Jim Davenport in Spartanburg, S.C., and Steve Peoples in Washington contributed to this report.
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