Thompson, who had launched an aggressive attack against Huckabee's record during Thursday night's GOP debate in Myrtle Beach, S.C., responded by insinuating that Huckabee is in truth nastier than his sunny demeanor, is unprepared for the presidency, and is making personal attacks while Thompson is "talking about issues concerning this country."
Huckabee has "raised enough money now to get some hit pieces and dredge up personal stuff and personal accusations against me," Thompson told CNN. "And now you're seeing the real Mike Huckabee come out. So, I think we've done a favor to the American people. Because these are serious times, and they require somebody that knows what they're doing and doesn't walk into a situation with foreign representatives and heads of foreign nations with training wheels on."
Told what Thompson said on CNN, Huckabee told reporters at the Greenville/Spartanburg Airport in Greer, S.C., Sunday afternoon, "Well, it seems like its perfectly okay for he or others to fire away these lengthy salvos at me, but if I respond then it's a personal attack. If you're going to play big league ball, you have to stand at the plate as well as throw a few, and that's just the way it works. If you really can't handle that, you probably shouldn't run for something as serious as president."
Since 1980, no Republican has won the presidency without first winning the South Carolina primary. But in this year's unpredictable GOP contest, with any number of possible nominees and no clear frontrunner, the South Carolina primary has taken on extra importance -- for Huckabee and Thompson in particular.
Huckabee needs to demonstrate that his Iowa caucus victory Jan. 3 wasn't a fluke, and that his scotch-tape-and-rubber-bands campaign is capable of going national. For his part, Thompson needs to win somewhere. Anywhere.
Addressing the substance of Huckabee's charges, Thompson Sunday acknowledged he was "in a law firm that did some lobbying work for Libya," but his involvement was minimal. He said he'd registered with the government because of "five minutes' worth of contribution" to discussions about another client, Haiti.
"It was totally consistent with the policies of this country, where a dictatorship had taken over that country and we were opposing that," Thompson said.
During the Republican debate Thursday night, Thompson -- about whom even his supporters complain of less-than-energetic campaigning -- showed remarkable pep and vigor, attacking Huckabee for having overseen a net tax increase as Arkansas governor, for having pushed merit scholarships for the children of illegal immigrants, and for having suggested he would sign a nation-wide ban on smoking in public places. He took issue with comments Huckabee made that the Bush administration had demonstrated an "arrogant bunker mentality" in its foreign policy.
"On the one hand, you have the Reagan revolution," Thompson said during the debate. "You have the Reagan coalition of limited government and strong national security. On the other hand, you have the direction that Gov. Huckabee would take us in. He would be a Christian leader, but he would also bring about liberal economic policies, liberal foreign policies. .. That's not the model of the Reagan coalition. That's the model of the Democratic Party."
Huckabee didn't respond much during the debate, but appearing on MSNBC's "Morning Joe" Friday morning, he took his well-known wit literally below the belt, joking, "I think Fred needs some Metamucil. I think it would help a lot. He was in a bad mood last night."
Campaigning Friday in Michigan, Huckabee went on the attack more substantively.
"It was real interesting hearing Fred Thompson talk about Ronald Reagan last night," Huckabee said. "Because Fred Thompson supported [then-President] Gerald Ford in 1976 and not Ronald Reagan. He supported [then-Sen.] Howard Baker in 1980 and not Ronald Reagan. I appreciate his recent conversion, but some of us were for Ronald Reagan back in the early days; our legacy goes back a little further."
Huckabee also tried to paint Thompson as having been an undistinguished senator.
"Eight years is a pretty long time to get a check from the federal government and not be able to say" he was responsible for any major legislation, Huckabee said.
On Saturday, Thompson called the criticism of his previous support of Ford and Baker as "kind of silly. Howard Baker was my mentor and personal friend in Tennessee for years and years. If you check the record, Gov. Huckabee supported Democrats on a fairly consistent basis in his days in Arkansas politics. I don't think he wants to get into that discussion. We'll see."
Of Huckabee's Metamucil's joke, on Sunday morning Thompson said "his response was to return fire with some potty humor. That's the best he could come up with for the last three days."
He added that he was happy to compare his record to Huckabee's, whom he described as "having raised taxes $500 million more than he cut." He described Huckabee's criticisms of the Bush administration as "blame-America-first comments," and pointed out, correctly, the Huckabee campaign chairman Ed Rollins had called the Reagan coalition dead.
Huckabee, Thompson charged, "talked around the subject and smiled and giggled and told a couple of jokes. When I came back, I said, 'You know, this is about the heart and mind of the Republican Party, because I don't believe it [the Reagan coalition] is [dead].'"
Said Huckabee, "The Writers Guild strike needs to end soon. Fred's got to get some better lines. Calling me a liberal would be laughable in Arkansas, where people recognized -- if anything, they called me this ultra-conservative guy. ... It's always interesting to me, when people get desperate, they start grabbing for anything."
Thompson responded that he had been asking questions about Huckabee's support for closing down the prison at Guantanamo Bay, his support for public programs for the children of illegal immigrants, and the fact that he was endorsed by a teachers' union.
"These are substantive issues," Thompson said. "These are not personal attacks. If the governor wants to get into personal attacks and things that happened some years ago and things that they've done and allegations, there's enough on the record in Arkansas that will keep us busy for the rest of this campaign."
Or at least until Saturday.
ABC News' Christine Byun and Kevin Chupka contributed to this report.