Nashville, Tenn. -- Newt Gingrich said there are "profound reasons" why Rick Santorum lost his re-election bid in 2006, painting a picture of a two-term senator who took positions that would make it "hard for him to carry that all the way to the general."

"He voted for the unions over FedEx," Gingrich told a luncheon of supporters. "I suspect most folks in this state don't know that. But in fact, he was a big labor Republican in Pennsylvania and I suspect when you get to Memphis and you say this is a guy who wanted to guarantee that FedEx gave into the unions, Santorum won't be as popular the following morning."

Recent polling indicates Gingrich is in fourth place here in Tennessee, which is one of the Southern states the candidate is relying on to restore momentum in his campaign. Gingrich said he believes he can do better in this state than the polls indicate, and predicted that after the results in Michigan and Arizona Tuesday, the contest for the Republican nomination will "redefine itself once again."

"We have now outlasted Pawlenty, Bachmann, Trump, Perry, Cain twice," Gingrich told the crowd - emphasizing the ability of his candidacy to outlast the others. He said Santorum is currently enjoying the "national news media momentum" because he "went to three states nobody else was in."

"Santorum was fourth place for three consecutive states. He did something very intelligent. He took all of his resources, he skipped South Carolina, Florida, and Nevada, he went to three states nobody else was in, won the three states, one of which was a disaster for Romney because he dropped from 60 to 35 in Colorado. So Santorum now has got all the national news media momentum," Gingrich said in explaining to the audience why he wasn't farther ahead in the polls.

Gingrich had sharp words for Mitt Romney as well, in particular a proposal unveiled Friday that would gradually increase the Medicare eligibility age.

"It's all at the margins, it's all Mickey Mouse," Gingrich said. "You've got to think about fundamental change outside the current system because the current system doesn't' work. And if you're trying to fix, if you're trying to manage the current system, you get trapped in decay, and therefore you have to be much bolder than our party is used to being."