Columbia, S.C. – Newt Gingrich took aim at former Massachusetts Gov. Mitt Romney Sunday as he prepared to move his campaign to Florida following his decisive victory in the South Carolina Republican primary.

Also Sunday, Romney said he would make public his 2010 tax return and an estimate for 2011 on Tuesday, according to press reports. Gingrich had been calling on Romney to release his tax records. Romney previously said he would not make them public until April.

Speaking on NBC’s “Meet the Press,” the former Georgia congressman called Romney an “establishment candidate” and described himself as a “Reagan populist conservative going all the way back to the 1970s.”

“In Florida, my case is going to be very simple,” the former House speaker said. “You have a clear establishment candidate in Mitt Romney. Look where his money comes from. Look at his background. Look what he did in Massachusetts… I think Floridians would like somebody who speaks for them to Washington, not somebody who speaks for the establishment to them.”

Without mentioning Gingrich by name, Romney on Saturday took the former congressman to task for criticizing his former private equity firm, Bain Capital. Gingrich called Bain "exploitive."

"Those who pick up the weapons of the Left today will find them turned against us tomorrow," Romney said. "And let me be clear, if Republican leaders want to join this president in demonizing success and disparaging conservative values, then they are not going to be fit to be our nominee."

New Jersey Gov. Chris Christie, a key Romney supporter, appeared on the NBC program moments after Gingrich and compared Romney and Gingrich's experience.

“This is a guy who has never run anything,” Christie said of Gingrich. “I don’t think on-the-job training should be the presidency of the United States. The fact of the matter is I don’t believe his record stacks up to Gov. Romney’s record in that regard.”

Gingrich was preparing to attend Mass in Northern Virginia Sunday and arrive Monday in Florida, where Republican voters will pick their nominee on Jan. 31. Gingrich has 14 paid staffers and seven campaign offices in Florida, and he has a campaign chairman in all of the Sunshine State’s counties, a spokesman said. His Florida campaign is leaning heavily on Jose Mallea, who managed U.S. Sen. Marco Rubio’s 2010 race.

Gingrich declared victory in the South Carolina Republican primary late Saturday, pulling off a stunning upset over Romney. Gingrich prevailed in South Carolina despite Romney's much bigger campaign war chest. Romney was also leading Gingrich in the polls here until the former House speaker drew praise for several fiery debate performances, including one from Thursday night.

“Thank you to everyone in South Carolina who decided to be with us in changing Washington," Gingrich said before thanking his family and campaign staff in a Hilton conference room packed with supporters. "The biggest thing I take from the campaign in South Carolina is that it is very humbling and very sobering to have so many people who so deeply want their country to get back on the right track."

Gingrich criticized the news media and the Obama administration before praising Romney, U.S. Rep. Ron Paul of Texas and former U.S. Sen. Rick Santorum of Pennsylvania.

"If you look at the four of us," he said, "we are proof that you can come from a wide range of backgrounds. And in America you have a chance to make your case no matter what the elites think in New York and Washington."

Romney spoke to supporters just after 8 p.m.

"This race is getting to be even more interesting,” he said. “This is a hard fight because there’s so much worth fighting for….Tomorrow we’re going to move on to Florida.”

Santorum and Paul spoke moments later, vowing to press on with their campaigns.

South Carolina Republican Party Chairman Chad Connelly issued a statement congratulating Gingrich Saturday.

"Speaker Gingrich won a hard-fought victory in South Carolina," Connelly said. "He deserves great praise."

Gingrich was clearly having fun early Saturday evening before the polls closed, smiling widely and cracking jokes. He was met at each of his campaign stops Saturday by huge crowds of enthusiastic supporters. During a stop at Whiteford’s Giant Burger in Laurens he elicited laughter when he told scores of supporters to start reaching out to their friends in Florida.

“Look, if we are going to win a people’s campaign, it is going to be by having people,” he said. “So it is very important for any of you who have relatives, friends, classmates, people who you own a business with, random people you met on a trip one time...” Gingrich trailed off, but the crowd got the point.

Gingrich and Romney nearly crossed paths in Greenville Saturday morning as they traveled around the Palmetto State searching for votes in the final hours before the polls closed.

Gingrich was on his way to campaign at Tommy’s Ham House just as Romney was leaving the eatery. They missed each other by about 20 minutes. Gingrich's spokesman, R.C. Hammond, called the scheduling a coincidence. As Romney boarded his campaign bus emblazoned with the words “Conservative, Businessman, Leader,” supporters from both sides tried to drown each other out, shouting “Newt!” and “Romney!”

“Where is Mitt?” Gingrich asked as he arrived. “I thought he was going to stay and we were going to have a debate here.”

"This is a very, very important day in South Carolina," he continued. "We have an opportunity to nominate a genuine conservative who can debate and who can take it to Barack Obama."

Romney, meanwhile, took aim at Gingrich Saturday, according to press reports, calling on him to release records related to his role consulting for Freddie Mac, the mortgage giant some critics link to the real estate market collapse.

The former Massachusetts governor also wished Gingrich a sarcastic "happy anniversary," noting that it was 15 years ago today Gingrich was reprimanded and fined $300,000 for violating House rules.

In Greenville, Gingrich called the huge crowd that had gathered to see him “remarkable.” Hundreds crammed into Tommy’s to watch him speak.

Bonnie Dixon, a homemaker from Greenville, was among those who showed up to see Gingrich. She said she was torn between him and Romney and was hoping seeing Gingrich speak would help her decide. She was heading to her polling station following the event. She said she likes Romney’s business experience but credited Gingrich with strong debate performances.

“I am just having a hard time making up my mind,” she said before turning to Romney: “I don’t think he would go toe-to-toe with Obama as well as Gingrich.”

Helen Shockley, also of Greenville, said she preparing to vote for Romney Saturday morning.

"I like his character. I like his commitment to his wife and family," she said of Romney, adding about Gingrich: "He is a career politician and we need something different in the White House."

Scott Vanvick, a construction contractor from Greenville, said he voted for Gingrich Saturday morning.

"I think he is the most probable candidate to beat Barack Obama," Vanvick said. "I think he knows his way around Washington to get things done... In the debates we listened to, I think Newt Gingrich handled himself well on some sensitive subjects. Overall, I think he has the best plan to get things changed."

Sally Chardos of Blythewood, a Columbia suburb, said she woke up Saturday and called her friends and family -- she has five children and 13 grandchildren -- and urged them to get out and vote for Romney. Then, she changed her mind and voted for Santorum, and got back on the phone.

"I didn't originally say Santorum because of his age and experience," Chardos said of the still-boyish looking 53-year-old Santorum. "Then I thought of John F. Kennedy on the way over. It just bothered my conscience."

Chardos liked Santorum's stand on a key social issue.

"I like his views and the fact he is definitely pro-life," she said.

Chardos' husband, Hank, was solid for Gingrich.

"I just think his experience and whit are two important elements in the coming weeks," he said.

Scott Jeffers, too, found Gingrich's demeanor important.

"I found him to be abrasively honest," Jeffers said.

In Columbia at the Gentleman's Closet consignment shop, owner Dean Ellison was holding court with customers. The long-time Republican voted for Santorum.

"He doesn't have the baggage that the rest of them do," said Ellison, a former LaGrange resident who said he voted for Walter George for U.S. Senate in the 1950s.

Ellison was particularly critical of Gingrich, saying the former Georgia congressman angered him "when he hammered Romney with those negative ads."

He was also upset that Gingrich accepted millions from Freddie Mac.

A customer, John Camp of Columbia, retorted that Romney went on the attack first. Camp voted for Gingrich.

"I've been impressed with the manner in which he handled himself in the debates and how he's aggressively campaigned since Iowa," Camp said. "When he got attacked, he had no choice."

Camp believes a Gingrich win in South Carolina will propel Gingrich past the Jan. 31 Florida primary to Super Tuesday March 6, when Georgia votes.

"I can't predict what will happen," he said, "but it will be a two-man race."

Later Saturday morning, scores of supporters scrambled through driving rain to see Gingrich appear outside a polling station at Powdersville Middle School, southwest of Greenville.

Carl Settle of Spartanburg wore two Gingrich campaign buttons on his chest and sported a big cowboy hat, hoping Gingrich would notice him so he could shake his hand.

"He has the experience. Because he has done it before he can do it again more easily," said Settle, who owns a tree nursery. He said the other candidates are "not bold enough." He also said Gingrich should be forgiven for his past mistakes, including his extramarital affairs. "I believe in the Lord and I believe Newt has asked for forgiveness and I think we should forgive him for his past."

During his campaign stop in Laurens, Gingrich was having so much fun that he abruptly stopped his speech when Jordan-Shane Cash sidled up to the former congressman and his wife, Callista. Gingrich grasped the little boy’s hand and turned so Jordan-Shane’s mother could take a photo of them.

“Hello,” he told the boy. “Do you have a mommy with a camera?”

He asked the boy for his name. The boy said something that sounded like “Johnny Cash.”

Gingrich: “You are Johnny Cash?”

The crowd erupted in laughter.

Gingrich: “I thought Johnny Cash was much bigger.”

The boy responded: “Jordan Cash!”

Gingrich: “OK. I feel much better.”