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Matt Rourke, Associated Press
Republican presidential candidate, former House Speaker Newt Gingrich, accompanied by his wife Callista, waits to speak at a Tea Party Rally, Thursday, Jan. 26, 2012, in Mount Dora, Fla.

JACKSONVILLE, Fla. — Pointing toward an evening debate, Mitt Romney jokingly urged supporters Tuesday to "just storm in" and support him even if they lacked tickets. Newt Gingrich warmed up with a particularly strong attack on Romney.

Former Pennsylvania Sen. Rick Santorum and Texas Rep. Ron Paul also were sharing the stage for the second debate of the week and the last before the Florida primary next Tuesday.

Opinion polls show a close race between Romney, the former Massachusetts governor, and Gingrich, who was House speaker for two terms in the 1990s, and the two clashed repeatedly in Monday night's encounter in Tampa.

Gingrich's unexpected victory in the South Carolina primary last weekend upended the race to pick a Republican opponent for Democratic President Barack Obama in the fall, and Romney can ill afford another setback.

In the days since his loss, he has tried to seize the initiative, playing the aggressor in the Tampa debate and assailing Gingrich in campaign speeches and a TV commercial.

An outside group formed to support Romney has spent more than his own campaign's millions on ads, some of them designed to stop Gingrich's campaign momentum before it is too late to deny him the nomination.

Campaigning Thursday at a factory that is scheduled to close, Romney criticized Obama and avoided mentioning Gingrich.

But the evening debate was on his mind — particularly the makeup of the audience in the hall.

"There may be some give and take. That's always entertaining," he said. "If you all could get in there we'd love to see you all there cheering."

A voice from the audience responded that there were no more tickets, and Romney replied: 'No tickets? Just storm in."

Gingrich seemed far less confident as he unleashed an attack reminiscent of his rhetoric a month ago when he was being outspent heavily on television and falling sharply in the polls just before the Iowa caucuses.

He accused Romney and Restore Our Future, the independent group, of dishonest ads, and said, "This is the desperate last stand of the old order. This is the kind of gall they have, to think we're so stupid and we're so timid."

He later told reporters he decided to sharpen his criticisms after Romney released his tax returns. "Here's a guy who owns Freddie Mac and Fannie Mae stock," Gingrich said. "He owns a Goldman Sachs subsidiary, which is foreclosing on Floridians. And on that front he decides to lie about my career? There's something about the hypocrisy that should make every American angry."

Romney released his income tax returns for 2010 and an estimate for 2011 after declining to do so in South Carolina.

Gingrich, also under pressure, disclosed the consulting contract one of his firms had with Freddie Mac, the government-backed mortgage giant that played a role in the foreclosure crisis that hit Florida especially hard. It showed payments of $300,000 in 2006 for unspecified consulting services.

Romney has pummeled Gingrich in the days since, calling him an influence peddler and a lobbyist who was taking money from the very organization that was harming Floridians.

Associated Press writers Brian Bakst and Kasie Hunt contributed to this story.