COLUMBIA, S.C. — With polls showing Newt Gingrich gaining ground on Mitt Romney, his campaign Wednesday accused the former House speaker of being too "chaotic" to lead the Republican Party or the country.
Mr. Gingrich, meanwhile, warned supporters that he expects the former Massachusetts governor to be "unendingly dirty and dishonest" in the run-up to Saturday's primary here.
Mr. Romney is trying to win his third consecutive state and once again head off his more conservative challengers, which some of those candidates said would essentially mean the end of the nomination battle.
In another sign that the general-election fight could be coming sooner rather than later, President Obama's campaign told the Associated Press that it was already purchasing advertising time in six states expected to be critical to his re-election effort.
The White House also announced plans to visit five key states in the wake of next week's State of the Union address.
Mr. Romney didn't get involved himself in the attacks on Mr. Gingrich, but instead kept to his standard speech. But his campaign organized a conference call with two surrogates early in the day to fire another salvo at Mr. Gingrich, who is fresh from a compelling debate performance Monday.
In a devastating critique of his time as speaker, former Rep. Susan Molinari, a New York Republican who was on the House leadership team with him in the 1990s, said Mr. Gingrich's insistence on being the focus of the political debate led to President Clinton's re-election in 1996 and Democrats' gain of House seats in 1998.
"When Newt is in the room, Newt becomes the focus," she said. "The issue has to be President Obama's performance in office and the steady hand of the candidate running against him."
Former Sen. Jim Talent, a Missouri Republican who also served in the House under Mr. Gingrich, recalled that after the 1994 election, when Republicans were planning welfare reform, Mr. Gingrich publicly tied that effort to orphanages with his famous "Boys Town" comments.
"I had to spend two months at the end of 1994, again before we were even being sworn in, putting that to bed because the welfare bill had nothing to do with orphanages," he said. "He almost killed that bill before it was even born."
Mr. Gingrich had scheduled a late-morning news conference in Columbia to talk with reporters, but canceled it. Instead, his campaign issued a statement pointing to some current and former members of Congress who have endorsed him, saying that shows he can be a leader.
On the campaign circuit in the afternoon, though, he told a crowd of supporters to be ready for more attacks.
"I fully expect the Romney campaign to be unendingly dirty and dishonest the next four days," he told a crowd spilling out onto the front porch of Bobby's Bar-B-Q in Warrenville, near the Georgia border.
Contrasting with Mr. Romney's surrogates' charges, he said when Republicans held the House in 1996 it was the first time the GOP had successfully defended a House majority since 1928.
Mr. Gingrich said he thinks Mr. Romney has internal polling showing him poised to lose in South Carolina on Saturday, and the latest public polls showed strong movement toward Mr. Gingrich.
"If we carry Saturday, I think I will become the nominee this fall," Mr. Gingrich said Wednesday.
Later in the day, Mr. Gingrich tried to undercut the case for voting for former Sen. Rick Santorum or Texas Gov. Rick Perry — the two other candidates seen competing in the primary-within-a-primary for the conservative vote.
"There is one candidate who can give you a conservative nominee and only one candidate who can stop Mitt Romney, and a vote for anyone else is a vote that allows Mitt Romney to potentially be our nominee," he said.
Rep. Ron Paul, Texas Republican, took the day off from primary campaigning to return to Washington to vote on the House floor against raising the federal government's borrowing limit.
Looming Thursday night is yet another debate, and Mr. Romney is sure to face renewed questions about his taxes.
In Monday's debate, he refused to agree to release his tax forms, saying he would revisit the issue in April. But by Tuesday he had changed course and said he would indeed release them later. At the same time, he acknowledged paying a tax rate that he said was closer to 15 percent at which the rate investment income is taxed rather than the higher rates many middle-class families pay on salary or wage income.
Mr. Gingrich told reporters Wednesday he paid income taxes at a rate of 31 percent.
On Wednesday afternoon, ABC News reported that Mr. Romney has up to $8 million invested in funds in the Cayman Islands, which it labeled a "notorious Caribbean tax haven." The report did not specifically say Mr. Romney was avoiding tax obligations, but stated that the revelation adds to questions about his income and wealth.
Andrea Saul, a spokesman for Mr. Romney, said the ABC report is erroneous.
"ABC is flat wrong," she said, adding that the investments in the Cayman Islands "are taxed in the very same way they would be if those funds were established in the United States. These are not tax havens, and it is false to say so."
• This article is based in part on wire service reports. Paige Winfield Cunningham reported from Spartanburg, S.C.
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