By Steve Holland
JACKSONVILLE, Florida (Reuters) - Is it too late for another Republican to jump into the 2012 U.S. presidential race?
Mitt Romney is riding high in Florida and threatening to take charge of the Republican nomination with a win in Tuesday's primary there.
But even as some party conservatives appear to be coming around to supporting him, many are concerned that the bitter fight between Romney and Newt Gingrich has damaged both of them to the extent that neither would be able to defeat Democratic President Barack Obama in the November 6 election.
Grassroots conservative activists are worried that Gingrich's attacks on Romney's business background have given Democrats a big hammer to use against the former Massachusetts governor this fall.
Meanwhile, mainstream Republicans think Romney is right when he says Gingrich is a Washington insider with deep personal and political baggage and more half-baked ideas than the corner pastry shop.
The Romney-Gingrich battle has left many Americans in a sour mood about the Republican contenders.
A Washington Post poll this week found that Romney and Gingrich each were viewed favorably by only about 30 percent of Americans.
So is there a chance that a popular Republican might come to the rescue and snatch the presidential nomination?
Analysts say there is still a sliver of time for another Republican candidate to jump into the race.
This year's campaign calendar is loaded with spring contests, meaning a Republican could enter the race in early February and still compete directly in states with at least 1,200 of the 2,282 or so Republican delegates, according to the University of Virginia Center for Politics.
It takes 1,150 delegates to win the nomination.
"If Republicans look at both Gingrich and Romney and think they can't win, it's an opening for another candidate," said Larry Sabato, director of the Center for Politics. "What that candidate has to do is win a series of big primaries and prove the point that this individual is electable, and that Republicans want a new candidate."
'THERE'S AN OPENING'
It would take a powerhouse politician to pull it off.
Think New Jersey Governor Chris Christie, for example. Or Indiana Governor Mitch Daniels, or former Florida Governor Jeb Bush.
Those three and other big names have repeatedly ruled out a 2012 campaign and seem content to wait until 2016, if a Republican does not win this year. Christie has endorsed Romney.
Anyone who did attempt to jump into the race would need to be able to muster large amounts of money and support quickly, and be more politically nimble than the last late entrant -- Texas Governor Rick Perry, who abandoned the race a week ago after poor performances in debates.
"There's an opening, but there's a big impediment," said Ipsos pollster Chris Jackson. "Any individual who wants to exploit that has to hit the ground at a full sprint."
Leading Republicans do not expect someone else to enter the race.
But they do foresee an increasingly aggressive movement to persuade conservatives to give up their flirtation with the fiery Gingrich and make peace with the more moderate Romney.
An example of this came Thursday from former Senate Majority Leader Bob Dole. He told National Review Online that when Gingrich was speaker of the U.S. House of Representatives, he "had a new idea every minute, and most of them were off the wall."
"If Gingrich is the nominee, it will have an adverse impact on Republican candidates running for county, state, and federal offices," Dole added. "Hardly anyone who served with Newt in Congress has endorsed him, and that fact speaks for itself."
Ari Fleischer, a Republican analyst who was a White House press secretary for President George W. Bush, told Reuters that a Gingrich victory in Florida's primary would have repercussions extending to the Republican nominating convention in Tampa in late August.
"If Newt wins Florida, I expect serious conversations to develop about how to stop Newt at the convention," said Fleischer, who is neutral in the 2012 Republican contest.
"My sense is that enough people who know Newt are scared of Newt winning. Enough congressmen and senators who have to run for re-election this year are scared at what he might do at the top of the ticket," he said.
One reason the battle has been so tough this year is because Republicans do not have an obvious choice as their nominee.
"We always have a competitive race and it always gets kind of rough when it narrows to two people," said Republican strategist Charlie Black. "The parlor game in Washington these days is, these guys are killing each other and we need to find an alternative candidate. It never happens. Since 1964 we've always been able to rally behind our candidate."
One complicating factor: Ron Paul.
The libertarian Texas representative is running fourth in the Republican race, behind the two leaders and former Pennsylvania senator Rick Santorum.
Paul has insisted he will not launch a third-party bid in order to rally his devoted supporters to his causes, which include a greatly reduced military presence overseas and budget cuts at home.
But he is leaving the door open, a crack.
A third-party bid by Paul could have a profound influence on the November 6 elections. A third-party effort by Texas businessman Ross Perot in 1992 contributed to incumbent Republican President George H.W. Bush's loss to Democrat Bill Clinton that year by drawing Republicans and independents from Bush.
Paul draws a mix of supporters across the political spectrum, from Republicans fed up with conventional candidates to anti-war Democrats.
Paul told NPR this week that "it's awfully premature" to say whether he will launch a third-party run.
"We have a few months to go before I will need an answer," he said.
(Additional reporting by Deborah Charles; editing by David Lindsey and Mohammad Zargham)