The race for the Republican U.S. presidential nomination is now focused on Florida, a sprawling southern state set to host the 18th debate between the remaining candidates on Monday night.

The two apparent leaders in the contest to pick a nominee to oppose President Barack Obama, a Democrat, in the national election in November are one-time venture capitalist Mitt Romney, a former governor of Massachusetts, and Newt Gingrich, a former speaker of the House of Representatives.

They each have captured one of the party's first two party primary elections. But Gingrich has the electoral momentum at the moment after last weekend's decisive upset victory over Romney and two other candidates in another southern state, South Carolina. New surveys of Republican voter sentiment in Florida show that Gingrich has quickly erased Romney's lead in the state in earlier polls and is now the frontrunner there.

Romney has started attacking Gingrich's House leadership in the late 1990s, which ended in his being fined $300,000 for an ethics violation and his eventual resignation from Congress.

Gingrich was fueled in his upset win in South Carolina by strong support from conservatives, some of whom say they are looking for a candidate willing to take on Mr. Obama in a forceful manner. Gingrich said Romney governed Massachusetts as a moderate with views on social issues that Republican voters would consider to be liberal. Gingrich, who led a Republican takeover of the House in 1994, said Romney has been struggling “to figure out how to find a version of Romney that will work.”

He told a television interviewer Monday that “you're going to see the establishment go wild in the next week or two” in opposition to his candidacy.

Several Republican contenders have dropped out of the nomination race after winning little electoral support and running short of cash to continue their campaigns. But two other candidates remain — a former senator from Pennsylvania, staunch conservative Rick Santorum, who last week was declared the winner of the caucus voting in Iowa in early January, and libertarian Ron Paul, a Texas congressman.

The new surveys of Republican voter sentiment in Florida show both of them trailing well behind both Gingrich and Romney.

All four candidates are set to face off in two debates this week, with another one Thursday.