JACKSONVILLE, Fla. (AP) - Pointing toward an evening debate, Mitt Romney jokingly urged supporters 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."