Charles Dharapak, Associated Press
Republican presidential candidate, former Massachusetts Gov. Mitt Romney, takes out food as he makes an unscheduled stop at Hudson's Smokehouse barbecue in Lexington, S.C., Wednesday, Jan. 18, 2012.

COLUMBIA, S.C. — Republican presidential candidate Mitt Romney is rolling out his closing appeal for votes in Saturday's South Carolina primary with an ad that takes swipes at President Barack Obama's economic policies and makes tough-to-keep promises.

The ad shows Romney giving his victory speech in New Hampshire's primary two weeks ago with his family in the background and mixes images from campaign stops on factory floors around the country.

"President Obama wants to fundamentally transform America," Romney says. "I stand ready to lead us down a different path. This president has enacted job-killing regulations; I'll eliminate them. He lost our triple-A credit rating; I'll restore it. He passed Obamacare; I'll repeal it."

Romney promises in the ad to cut, cap and balance the federal budget. "If you believe that the disappointments of the last few years are a detour, not a destiny," he says, "then I am asking for your vote."

The ad is a stark contrast to the harsh messages Romney and a political action committee supporting him have been using for weeks in South Carolina, a state whose Republican primary winner has gone on to win the nomination each time since 1980. South Carolina's primary is expected to thin the field before candidates rush to delegate-rich Florida, which holds its primary Jan. 31.

Television ads, mailers and phone messages have been rough. Mail pieces, for instance, have called challenger Rick Santorum a hypocrite for raising his pay while in the Senate and said former House Speaker Newt Gingrich launched an attack on America's free enterprise system by questioning Romney's business deals.

Romney's ad sets up several challenging policy initiatives for a Romney administration. Cutting the deficit, much less balancing the federal budget and capping spending, has been an elusive goal for a deeply partisan Congress. While Romney and other candidates complain about regulations killing jobs, businesses have cited the overall economy and slow consumer demand more frequently than regulations as the top problems. That suggests that rolling back regulations may not easily lead to job creation.

When Standard and Poor's downgraded the nation's AAA debt rating last year, it came after months of warnings about gridlock in Congress over dealing with the nation's financial problems. In a time of rising economic challenges, S&P said the U.S. had weakened "effectiveness, stability and predictability" in its policymaking and political institutions. It is far from clear when and how those shortcomings will be repaired.

The new federal health care law that Obama pushed through over GOP objections will have key elements tested in the Supreme Court this year. Even if those elements fail, facets of the health care law are popular and may never be repealed, including ending lifetime maximum policy limits and extending coverage under a parent's health insurance policy to children until they're 25.

Follow Jim Davenport on Twitter at