Former Speaker of the House Newt Gingrich speaks to guests...

Former Speaker of the House Newt Gingrich speaks to guests gathered for a campaign stop at the National Toy Farm Museum in Dyersville, Iowa. (Dec. 27, 2011) Credit: Getty Images

No more Mr. Nice Guy.

Republican presidential candidate Newt Gingrich lambasted two of his top GOP rivals on Tuesday, despite his claim that he's sticking to a positive campaign.

Gingrich said he couldn't vote for Ron Paul if he were to become the GOP nominee and called the Texas congressman's views "totally outside the mainstream of every decent American."

In the same interview on CNN, Gingrich also offered a testy rebuke to Mitt Romney, saying that if Romney wants to run a negative campaign attacking Gingrich he should at least be "man enough to own it."

The sharp comments come as the former House speaker has seen his support slip in Iowa amid a barrage of attack ads that have cast him as an ethically challenged Washington insider.

Scrambling to regain momentum, Gingrich and a political action committee supporting him each took the wraps off television spots that will run statewide in Iowa.

The PAC Winning the Future is composed of former Gingrich staffers. The ad, its first, includes a broadside at Romney, although the former Massachusetts governor is never named.

"The Republican establishment wants to pick our candidate," the ad says. "When a principled conservative took the lead, they outspent Newt Gingrich 20 to 1, attacking him with falsehoods. ... Don't let the liberal Republican establishment pick our candidate."

Gingrich has said he will disavow any independent political action committee that spends money on negative ads. His own spot, funded by his campaign coffers, focuses on jobs and economic growth.

The former Georgia congressman launched a 22-stop "Jobs and Prosperity" bus tour, which kicked off Tuesday in Dubuque, in the northeast corner of Iowa. But he found himself on the defensive again on health care as a new memo surfaces that showed he had once praised the law enacted in Massachusetts when Romney was governor.

In an April 2006 memo from Gingrich's Atlanta-based Center for Health Transformation, he called it "the most exciting development of the past few weeks." He also said the law had "tremendous potential to effect major change in the American health system."

The memo also noted shortcomings in the Massachusetts law. Gingrich said the state's many regulations prohibited insurers from offering cheaper plans that would make coverage affordable. But he went on to note that that "we agree entirely with Gov. Romney and Massachusetts legislators that our goal should be 100 percent insurance coverage for all Americans."

Gingrich and others have argued that the Massachusetts law, widely seen as the model for President Barack Obama's national health overhaul, undercuts Romney's conservative credentials. Gingrich also has faced questions about his past support for an individual health care mandate, anathema to conservatives.

A Gingrich spokesman said Gingrich's comments are "old news that has been covered already."

"Newt previously supported a mandate for health insurance and changed his mind after seeing its effects," said the spokesman, R.C. Hammond. "The real question is why 'Mitt the Massachusetts Moderate' won't admit that health insurance mandates don't work."

The Gingrich memo was first reported Tuesday by The Wall Street Journal.

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