Newt Gingrich chided his GOP presidential opponents in a new TV ad for going negative but conceded later Thursday that the attacks could well take a toll on his support in the run-up to the Iowa caucuses on Jan. 3.

"I would be very surprised if we didn't see some ups and downs over the next three weeks," the front-running former House speaker told Iowa Public Television.

Gingrich commented hours before he and six rivals were to meet in Sioux City for their final pre-caucus debate, with Gingrich intently focused on staying ahead of the pack and the others trying anew to derail him.

The debate will be a crucial moment for him to show poise in the face of the attacks, Republican Iowa Gov. Terry Branstad told The Associated Press.

Branstad said he was unlikely to endorse a candidate and was unsure whether Gingrich has what it takes to be president.

"I think he's a great idea person. I have a lot of respect for him," Branstad said. "But whether he has the discipline and the focus, I don't know."

Chief rival Mitt Romney and his allies are waging an aggressive effort to discredit Gingrich in the eyes of conservatives at campaign events, media interviews and through independent advertising. Ron Paul also is going after Gingrich on television, and Michele Bachmann, Rick Perry, Rick Santorum and Jon Huntsman have sharpened their criticism.

Campaigning later in Sioux City, Gingrich responded to Branstad's comment by suggesting Branstad "watch and decide," and said he had "no idea" why the questions persist about his discipline.

He ticked through a list of accomplishments he suggested required discipline, such as leading the 1994 Republican takeover in the U.S. House, passing four consecutive balanced budgets, and helping enact welfare reform with Democratic President Bill Clinton in the 1990s.

"It would strike me that is reasonably good proof of discipline," Gingrich told reporters after addressing a high school government class.

Perry's campaign piled on Thursday with a new television ad in Iowa that casts both Gingrich and Romney as Washington insiders lacking conservative credentials. Perry is portrayed as an outsider in an attempt to make the struggling candidate more appealing to voters who've have had it with career politicians being in charge in Washington.

"Gingrich and Romney. Insiders," a voice says in the spot, adding that Perry's plan to create jobs and overhaul Washington "make him the outsider political insiders fear most."

Former Pennsylvania Sen. Rick Santorum has been picking up support among Iowa's influential social conservatives, but he has not yet begun running ads. A political action committee unaffiliated with Santorum's campaign but supporting him, called the Red, White and Blue Fund, has purchased $200,000 in television time in Iowa for a spot describing Santorum as "the true conservative you can really trust."

In Gingrich's latest ad, he said voters want to hear politicians offer solutions for the nation's problems, not personal attacks.

"These are challenging and important times for America. We want and deserve solutions," Gingrich said in the ad running in Iowa, trying to stay above the fray while still poking at his opponents. "Others seem to be more focused on attacks rather than moving the country forward. That's up to them."

Despite the attacks, Gingrich said Thursday that he has surged ahead because voters are looking beyond his troubled past for a candidate who has had big achievements. Some of Gingrich's rivals have tried to exploit his confessions of marital infidelity, three wives and ethical problems while in Congress.

"I think voters have rendered judgment and they understand my weaknesses and they understand my strengths," Gingrich said in a taped interview with Iowa Public Television. "They believe that at a time when the country is in deep trouble they want somebody who has big solutions and somebody who has a track record of getting big things done."

Gingrich took credit for balancing the federal budget and overhauling welfare as speaker and said those accomplishments outweigh his negatives. They also were achieved through cooperation with Clinton.

"It's a balanced judgment and I'm very open to people getting to know me and getting to understand me," Gingrich said. "Part of it is that people accept the sincerity of my willingness to talk about my life."

Gingrich also told the Iowa station he regretted attacking Romney during a weekend debate, calling it "foolish."

At Saturday's debate, Romney said the biggest difference between them is that he offers decades of private-sector experience while Gingrich is a Washington insider.

Gingrich countered that Romney would have become an insider, too, had he not lost a 1994 U.S. Senate bid. "The only reason you didn't become a career politician is because you lost to Ted Kennedy in 1994," the former House speaker said.

Gingrich said Thursday: "I do regret taking a shot at Mitt. It was foolish on my part."

With time running short, Romney's campaign redoubled efforts to cast Gingrich as an unreliable leader on a host of fronts.

A web video by Romney's campaign shows an old clip of Gingrich praising Romney as someone who has created more jobs in the private sector than President Barack Obama's entire Cabinet. In a new Iowa television ad, Romney says it's a "moral responsibility to believe in fiscal responsibility," which could be taken as a swipe against Gingrich.

Romney also has criticized Gingrich for calling Rep. Paul Ryan's Medicare plan, which is popular among conservatives, "right-wing social engineering

Romney's campaign on Thursday also highlighted support from former Reagan administration officials, including names that had been previously announced.

The announcement was a jab at Gingrich, who has begun been to sell himself as a "Reaganite." After last weekend's debate, Gingrich's campaign immediately issued a statement declaring, "Newt Gingrich claims the Reagan mantle."

Appearing in Fort Dodge, Gingrich told a questioner that he would support efforts to prohibit members of Congress from using insider information to get rich. A spokesman said later that Gingrich was not endorsing any particular proposal.

A bill that would impose such a provision on lawmakers is pending in the Senate.

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Associated Press writers Shannon McCaffrey in Fort Dodge, Iowa, and Thomas Beaumont in Sioux City, Iowa, contributed to this report.