That gives Florida the feel of a two-man race, and Romney and Gingrich are treating it that way. The two men sparred heatedly Monday night in a debate that virtually relegated Santorum and Paul to supporting roles.
A second debate is set for Thursday in Jacksonville. And if their separate appearances during the day on the Spanish-language television network Univision is a guide, it will be as feisty as the first.
Gingrich referred acidly to Romney describing a policy of "self-deportation" as a way of having illegal immigrants leave the country without a massive roundup.
"You have to live in a world of Swiss bank accounts and Cayman Island accounts and automatically $20 million income for no work to have some fantasy this far from reality," he said, referring to some of the details disclosed this week when the former Massachusetts governor released his tax returns.
"For Romney to believe that somebody's grandmother is going to be so cut off that she is going to self-deport, I mean, this is an Obama-level fantasy."
Romney's campaign swiftly produced evidence that aides to Gingrich had used the term "self-deport" approvingly, and the former governor attacked.
"I recognize that it's very tempting to come out to an audience like this and pander to the audience," Romney said. "I think that was a mistake on his (Gingrich's) part."
Gingrich also ran into trouble over a radio ad his campaign was airing that called Romney "anti-immigrant." Sen. Marco Rubio, R-Fla., who is neutral in the presidential race, criticized the commercial, and Romney said the term "anti-immigrant" was an epithet.
For Obama, Iowa was the first of five stops in three days following a State of the Union speech in which he stressed the theme of income equality that is expected to be one of the cornerstones of his re-election campaign. He also wove in proposals to help restore the U.S. manufacturing base that has withered in the course of the recession that began in 2008.
"Our economy is getting stronger, and we've come too far to turn back now," he told workers and guests at a conveyor manufacturing plant in Cedar Rapids. Speaking of Republicans, he said, "Their philosophy is simple: We're better off when everyone is left to fend for themselves and play by their own rules."
It's a message that may be received differently depending on the local economy.
Iowa's unemployment was most recently measured at 5.6 percent, well below the national average. In Arizona, which has its primary in four weeks, joblessness is 8.7 percent, while Nevada's at 12.6, the highest in the country. Its caucuses are Feb. 4.
Associated Press writers Brian Bakst and Kasie Hunt in Florida contributed to this report.
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