(CNN) - Newt Gingrich on Friday urged Mitt Romney to go after President Barack Obama in next month's debates with a gusto the former House speaker knows well.
"When he walks in to debate Obama, he's got to be as tough with Obama as he was with me in Florida," Gingrich said in an interview on CNN's "Piers Morgan Tonight."
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After all, Gingrich said, Romney "is not in a competition to be likeable."
At two debates in Florida last January amidst their bitter struggle for the GOP presidential nomination, Romney lit into Gingrich.
The two entered the Florida primary locked up in the polls. But after some heavy stumping - and arguably some debate thumping - Romney emerged on top in the vote count, beating Gingrich by 14 points and claiming the state's delegate haul.
With Romney trailing Obama in favorability, Gingrich encouraged Romney to play aggressively on the debate stage. The most recent CNN/ORC International Poll of likely voters, conducted earlier this month after the conclusion of both conventions, showed Obama with a 9 point advantage over Romney in their respective favorability ratings.
"He's in a competition to be capable," Gingrich said. "We need somebody who can turn America around. We need him to convince us that a Romney recovery is better than an Obama stagnation. Unless he can do that, I don't care how much effort they spend trying to make him likeable - it won't work.
Appearing separately on the program, Maryland Gov. Martin O'Malley argued that Obama has produced more than stagnation.
"I think the polls show overwhelmingly that most of us understand that the wrecking of our economy was the result of policies that were inflicted upon us during the Bush years," he said. "We've now had 30 months in a row of positive private sector job growth. Foreclosures are now lower than they were before President Obama took office. And while we still have a lot of work to do, we are headed in a much better direction than we were the day he took that oath."
In the interview, Gingrich also responded an apparent contrast between Romney's comments that he had not - and would be disqualified from the presidency if - he paid more in his taxes than he owed, and his campaign's acknowledgement that he could have paid less had he reported all of his charitable giving.
"I don't pay more than are legally due and frankly if I had paid more than are legally due, I don't think I'd be qualified to become president," Romney said in a July interview. "I'd think people would want me to follow the law and pay only what the tax code requires."
But documents released Friday showed the Republican presidential nominee reported on his 2011 tax return that approximately 16% of his income went to charity, while his campaign said the actual amount was 30%.
Gingrich initially laughed and took a swipe at Vice President Joe Biden, charging that the vice president ought to then "resign this evening because he has said enough different goofy things over time that you couldn't possibly remain vice president."
Then, Gingrich described Romney's charitable giving as a credit to the GOP candidate.
"I think it is a good thing for Romney," Gingrich said. "Apparently he's done this his whole life, to have a very substantial donation process for charities, for his church, and for things he wants to do voluntarily as a citizen. That's also a kind of self-tax to keep civilized society moving."
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