WASHINGTON — Republican presidential hopeful Mitt Romney charged Friday into the final weeks before the leadoff Iowa caucuses, unshaken by Newt Gingrich, the race's leader, and trying to stem the former House speaker's rise in key states.

Romney campaigned in western Iowa, where he had delivered a steady debate performance the night before, stopping short of the attacks on Gingrich that had marked the former Massachusetts governor's campaign for the past week.

While Gingrich took a day off the campaign trail, Romney claimed a coveted endorsement from South Carolina Gov. Nikki Haley, a tea party darling. The state holds the first-in-the-South primary in late January and Gingrich, a former congressman from neighboring Georgia, has organized and campaign aggressively there.

Romney also began airing new ads in New Hampshire and South Carolina on a day that amounted to a show of force for him. He is targeting Gingrich in the top three states with less than three weeks to go before voting begins in Iowa on Jan. 3.

"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 in a statement after announcing her endorsement on Fox News Channel.

She later told The Associated Press that Romney "has led in making decisions."

The two were to appear together in South Carolina on Friday and Saturday.

In the AP interview, Haley said the large GOP field has strengths and weaknesses.

"We don't have a perfect candidate," she said. She said she liked Romney's ability as governor to work with Democrat, business background and outlook on health care.

Haley's nod is somewhat rare because sitting governors of important primary states often remain neutral. Iowa's GOP Gov. Terry Branstad has said he does not plan to endorse a candidate. Branstad said Thursday that he wasn't sure Gingrich had the discipline to be president, but he also has criticized Romney for not campaigning all-out for the caucuses.

Romney has focused heavily on winning New Hampshire's first-in-the-nation primary on Jan. 10. But he has been spending more time in Iowa as Gingrich has risen in the polls, and has aired TV ads promoting his candidacy and distributed mailers attacking Gingrich.

"I need your help at the caucus," Romney told about 80 Republican activists and employees at a Sioux City steel company on Friday.

Romney's new ad in New Hampshire shows the former business executive talking to voters about their economic concerns. In the ad running in South Carolina, Romney touts his leadership and describes himself as "a man of steadiness and constancy."

Unlike his all-out but ultimately unsuccessful attempt to win the 2008 caucuses, Romney hopes a better-than-expected showing among Iowa conservatives could lift him going into New Hampshire.

But Romney is also looking increasingly beyond Iowa, advisers said.

Sensing a flattening in Gingrich's support, Romney stayed positive Friday and looked to step up his effort in South Carolina in hopes of disrupting Gingrich's plan.

That strategy poses risks for Romney, whose Mormon faith and changed positions on social issues gives some South Carolina GOP activists pause — as in socially-conservative Iowa.

Romney's attacks on Gingrich's judgment and temperament over the past week, and the aggressive criticisms by GOP rivals Michele Bachmann and Ron Paul, have cut into Gingrich's lead in Iowa in a way that could weaken him in next-up New Hampshire.

Taken together, it suggests slowing Gingrich's rise in Iowa could prevent him from going into South Carolina in a position of strength.

In Thursday's debate, Romney pivoted from the attacks he's been leveling against Gingrich and left it to others to pile on.

The fast-paced debate underscored the state of the race, with Gingrich leading in the polls nationally and in Iowa and his pursuers working on multiple fronts to overtake him.

The candidates — except for Gingrich — were making final pitches to voters on Friday before people begin focusing on the holidays.

Rep. 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.

"I am the only consistent, constitutional conservative," Bachmann said, beginning a bus tour through Iowa's 99 counties. "I'm not a convenient conservative."

She predicted the retail campaigning she's doing on the bus tour would help her do well in Iowa and that would "be a cannon shot into South Carolina."

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 pre-recorded political messages, or "robo-calls," to contact residents on a national do-not-call list.

Gingrich's campaign denied wrongdoing.

Haley's endorsement, meanwhile, could help Romney in her state, which is third in line to pass judgment on the GOP field. How much it could help, however, is unknown.

Governors can use their statewide political networks to help presidential candidates. But polls show Haley is not as popular as she was following her November 2010 election.

Even so, she remains a favorite of tea party activists whose energy helped Republicans win across the country last fall. Their enthusiasm will be critical in helping the GOP presidential nominee next year, but Romney has struggled to court them.

South Carolina is a difficult state for Romney. He competed aggressively there during his first presidential run in 2008 only to bail out shortly before the primary. He had failed to ease voter concerns about his faith and reversals on social issues.

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, a year when the tea party wielded big clout in key races across the country, including hers.

Associated Press writer Jim Davenport in Spartanburg, S.C., contributed to this report.