It’s no-holds-barred in the GOP presidential primary.

Candidate for the Republican Presidential nomination Former Speaker Newt Gingrich enters a townhall style gathering in Manchester, N.H., Monday, Jan. 9, 2012. (Melina Mara/THE WASHINGTON POST)

Former House speaker Newt Gingrich on Monday took aim at former Massachusetts governor Mitt Romney’s tenure at the helm of Bain Capital, arguing that his rival for the presidential nod “owes all of us a press conference” to explain the private equity firm’s downsizing of companies.

“If we have a potential nominee who can’t take the heat in February you sure don’t want to discover that in September so I think Governor Romney owes all of us a press conference where he explains what happened to the companies that went bankrupt and why did Bain make so much money out of companies that were going bankrupt,” Gingrich told Fox News Channel’s Shepard Smith.

The remarks from Gingrich follow similar comments by Texas Gov. Rick Perry, attempting to seize on a Monday morning campaign-trail misstep by Romney, who told a breakfast forum, “I like being able to fire people who provide services to me.”

“If you’re a victim of Bain Capital’s downsizing, it’s the ultimate insult for Mitt Romney to come to South Carolina and tell you he feels your pain. Because he caused it,” Perry said in Anderson, S.C.

And former Utah governor Jon Huntsman’s (R) senior strategist John Weaver argued that on Monday, Romney “reminded voters why he’s one of the weakest frontrunners in presidential history.”

“’I like being able to fire people’ doesn’t exactly scream electability,” Weaver said in a statement. “History shows that nominating a gaffe-prone, out-of-touch, flip-flopping, inauthentic candidate is a losing strategy. Yet, John Kerry’s legacy lives on with Mitt Romney. Voters are looking for someone they can trust. That’s Jon Huntsman, not Mitt Romney.”

As the GOP primary attacks step up, Gingrich took aim at Romney for negative ads that were run against him in Iowa and elsewhere.

“In South Carolina and Florida you’ve already got Romney negative ads running,” Gingrich said. “I mean he’s gone in early, spending lots of money. His idea is that he is going to shrink his opponents down to his size because he can’t grow.”

He also brushed off Wall Street Journal columnist Peggy Noonan’s depiction of the former House speaker as “an angry little attack muffin” in light of his response to the onslaught of negative ads.

“Well you know any time somebody uses the word little about me I am so grateful that it’s a little hard for me to be particularly angry about it so I am not going to comment negatively,” Gingrich said.

“All I will tell you is Governor Romney, I spent three weeks saying let’s be positive, I spent three weeks saying directly to Governor Romney and the media, why don’t you pull the ads. When we were positive I was ahead by a huge margin because the ideas I was offering, the Reagan conservatism I was offering was winning.”