This tactic is now being used by Romney against Gingrich. The Washington Post's Greg Sargent posts this flyer, at left, mailed to voters in Florida by the Romney campaign that points to Gingrich's "well of sleaze." Utah Rep. Jason Chaffetz, a Romney backer, told Politico's Alex Isenstadt and Jake Sherman Friday that the idea of Gingrich winning the Republican nomination "scares me to death... Newt Gingrich is an unreliable leader. He’s prone to becoming unhinged. He’s been mired in scandal in his personal and professional life. And he is a consummate D.C. insider." New Jersey Gov. Chris Christie called Gingrich an embarrassment. During Thursday night's debate, Romney called Gingrich's claim that he was anti-immigrant "repulsive."

Gingrich has a tougher time making this case against Romney, who has been married only once. But that doesn't stop him from trying. In Thursday's debate, Gingrich portrayed Romney as greedy and depraved, saying Romney had invested in firms that profited from foreclosing on Floridians. "So maybe Governor Romney in the spirit of openness should tell us how much money he's made off of how many households that have been foreclosed by his investments?" he asked.

2. Corruption

Gingrich took down Democratic incumbents by accusing them of violating ethics rules. He brought ethics charges against Speaker Jim Wright in 1988 (Wright resigned). He was involved in the House postage scandal that brought down Dan Rostenkowski. He pushed for an investigation into the House banking scandal, in which members of Congress -- including Gingrich himself -- bounced checks from their House bank accounts. And, of course, he led the impeachment of President Clinton. Now Romney is portraying Gingrich as a corrupt creature of Washington. On Gingrich's consulting work for Freddie Mac, Romney said at the debate, "You can call it whatever you like -- I call it influence peddling. It is not right. It is not right." The reverse side of the mailer Sargent posted, at right, calls him unethical.

Gingrich has tried to present his eat-the-rich attacks on Romney's business career as a question of ethics. Romney was "looting companies," Gingrich said. "It’s not fine if the person who is rich manipulates the system, gets away with all the cash and leaves behind the human beings," he said earlier this month. This time, "the system" is finance, instead of Washington. "Romney owes all of us a press conference where he explains what happened to the companies that went bankrupt and why Bain made so much money out of companies that were going bankrupt."

3. Elitism

Since the Nixon era, Republicans have argued that uppity liberals want to impose their rules on hardworking, upstanding "traditional" families. It worked against John Kerry in 2004. Barack Obama played into this one in 2008, when he said the working class bitterly clung to guns and God, which offered quite the opening for Sarah Palin. Gingrich said of Romney this week, "I think you have to live in a world of Swiss bank accounts and Cayman Island accounts and automatic -- you know, $20 million a year of no work -- to have a fantasy this far from reality." Worse, Gingrich said in a campaign speech, Romney thinks you're a moron. Referring to Romney's questioning of his Reaganite credentials, Gingrich said, "This is the kind of gall they have to think we're so stupid and we're so timid... The message we should give Romney is, 'We aren't that stupid and you aren't that clever.'"