He also used a refrain he's repeated throughout the week questioning Romney's conservative credentials.
“Governor Romney was first an independent, then repudiated Reagan-Bush, then voted for Paul Tsongas, the most liberal candidate in the ‘92 campaign, then ran to the left of Teddy Kennedy in 1994,” Gingrich said.
He also noted that "three out of four Republicans rejected him" at the polls Tuesday night.
Earlier Wednesday, Gingrich told radio host Laura Ingraham that he could "absolutely" team up with Iowa second-place finisher Rick Santorum to take down Romney.
"Of course," Gingrich said. "Rick and I have a 20-year friendship. We were both rebels, we both came into this business as reformers. ... We'll both stay in the race for a while, we'll see how our personalities wear and how our policies and ideas wear."
He went on to question whether there was a ceiling on Romney support.
"And the thing that's interesting is if you take the votes, you add to that Perry and Bachmann, you begin to see the size of the conservative vote compared to Romney ... if you take, you know, Santorum and Perry and Bachmann and Gingrich you get some sense of what a small minority Romney really represents," Gingrich said.
Gingrich told supporters in New Hampshire that he didn't necessarily plan to match Romney's negative ads. But the former Speaker made clear that the claws would come out in what he predicted would be "a very lively campaign."
“We’re not going to go out and run nasty ads,” Gingrich said. “But I do reserve the right to tell the truth. And if the truth seems negative, that may be more a comment on his record."