The Iowa victories of Barack Obama and Mike Huckabee have touched off a mid-winter political heat wave in New Hampshire as their rivals crisscross the state trying to win the hearts and support of key independent voters before Tuesday’s primary.

The political climate threatens to get even hotter Sunday night when Republican hopefuls face off in a unique and freewheeling roundtable discussion on FOX News.

Watch FOX News at 8 p.m. Sunday for a roundtable discussion with five Republican presidential candidates.

The candidates are racing around the state to make their last-ditch pitches before a contest that comes close on the heels of Iowa's caucuses, in which Barack Obama and Mike Huckabee emerged victorious in their respective party votes. Not only will they have to reach their base, but 40 to 45 percent of the Granite State's voters are independent, and about 25 percent of Tuesday's electorate is expected to come from that bloc. Independents are an unpredictable bunch, however, tending to make up their minds on a candidate later than party regulars, and some may decide not to show up at all.

The number of independents leaning toward the Democratic Party has doubled since 2000 meaning the number of independent-leaning Republicans has fallen sharply. That could be good news for Obama, who has surged in the polls in the state in the last few days. It could also spell bad news for John McCain, who counted on independents to make up a significant portion of his 18-point win in the state against George W. Bush eight years ago.

McCain is hoping Connecticut Sen. Joe Lieberman's endorsement will help him with those independents. Lieberman bucked his own party and won re-election as an independent in 2006 after losing the Democratic Party primary to an anti-war candidate. While Lieberman remains a Democrat, McCain, who has steadily supported the U.S military effort in Iraq since its start in 2003, faces the challenge of winning over independents driven by their opposition to the war in Iraq.

Meanwhile, getting the crowds to listen to the candidate is among the biggest challenges for all of the contenders, and the bigger the crowd, the more potential pitfalls. Talking to voters on Sunday, McCain took a pounding in a well-attended town hall format over his opposition to President Bush's tax cuts in 2001 and 2003. New Hampshire voters are notoriously anti-tax, but they also hate government spending so McCain, also considered a deficit hawk, was walking a fine line in his answers, and even winning applause on several occasions.

Of course, the largest crowds to be reached are frequently on television, and so the Republican candidates are also revving up for their appearances at FOX News' roundtable discussion on Sunday evening.

The roundtable format will feature McCain, Mitt Romney, Fred Thompson, Rudy Giuliani and Mike Huckabee. Neither Ron Paul nor Duncan Hunter was invited to the discussion, causing widespread complaints from their supporters and the Paul campaign.

In the RealClearPolitics average of Republican polling in New Hampshire, McCain leads the pack with 32.7 percent compared to 28.1 percent for Romney, 11.4 percent for  Huckabee, 9.1 percent for Giuliani, 8 percent for Paul and 2.4 percent for Thompson. Nationally, Giuliani is on top with 20.8 percent, followed by McCain and Huckabee, both at 17.6 percent, 14.4 percent for Romney, 11.4 percent for Thompson and 3.6 percent for Paul.  

Huckabee won the Iowa caucuses but his performance in a debate Saturday night in New Hampshire was neither cheered nor jeered. On Sunday night, Huckabee's goal is to try to capture voters' imagination as he did in Iowa.

To that end, Huckabee has been slowly changing his rhetoric, offering a more populist message that hits on the Republican Party -- either the Bush administration's conduct in the war in Iraq and or a tax structure that he says he wants to change so that the rich don't become poorer but the poor become richer.

"I think the Republican Party needs some repair.  The Republican Party needs to remember that its strength was being the champion for small business.  Eighty percent of all jobs in this country come from small business," he told "FOX News Sunday." 

"If we become the party that forgets that, if we become the party that does not empower the individual who wants to struggle from his place at the lower end of the economic spectrum up the ladder, then we're going to lose a lot of the base that gave us great strength, that helped us to become the majority party, that built the Reagan coalition, that also helped elect both George Bush 41 and George Bush 43," he said.

Huckabee also hit on Romney, who has faced a series of attacks since before the Iowa caucuses last week. Romney also got a dressing down from all sides on Saturday night's debate.

Seen as the candidate whose support could be most easily siphoned off, it is essential for Romney to break out from under the criticism and drill down to the essence of his message, one of conservative values that also envisions a stronger economy and strengthening the U.S. image abroad.

Speaking on "FOX News Sunday," Romney said it's all well and good for McCain to attack his record, but the fact of the matter is he was successful as governor when it came to changing Massachusetts whereas McCain has been in Washington for 27 years and has battled for change unsuccessfully.

"He's somebody who wants to change Washington.  He talks about changing Washington.  But he's been there so long, he's got so many lobbyists at each elbow, he's worked so long -- in many cases, he's a maverick against his own party," Romney said.

He added that he has changed his mind on some issues, but those changes have been for the better.

"Everybody over time is going to make an experienced judgment based on what they see at the time or what they think is right, and no candidate has been the same throughout the entire process.  And if they have, I'll show you a candidate that ought to be pushed aside, because you know what?  You should learn from experience.  And if you want somebody who's never learned from experience, who's never made a mistake, I'm not your guy," he said.

Asked to respond Sunday morning, McCain declined to get into another repartee after Saturday night's withering upper cuts against Romney. 

In an effort to avoid any potholes on the way to Tuesday's primary, Romney has scaled down several of his events and has been attending smaller restaurant and diner-style events where he can reach people a more one-on-one basis, where he is credited for his personal appeal.

Both Giuliani and Thompson are hoping to skate out of New Hampshire for the most part unharmed. Thompson told FOX News on Sunday that he's not looking for a victory, and mostly is focusing on South Carolina where he is polling well. Rudy Giuliani's strategy is built on Feb. 5, when 19 states hold GOP contests. His national approach is an untested strategy, but his campaign says this year has an unusual election calendar.

On the Democratic side, Obama is seen as the strongest war opponent, and he has much to gain from dovish independents willing to vote in the Democratic primary, as well as his portraying Hillary Clinton as part of the Washington, D.C., establishment. On Sunday, Obama won the endorsement of former New Jersey Democratic Sen. Bill Bradley, who ran as the liberal alternative to Al Gore in 2000, and lost, polling data suggest, because independents broke for McCain at the time.

But Obama's advisers are optimistic. The latest RealClearPolitics average of Democratic polls in New Hampshire shows Obama with 34.2 percent compared to 30.9 percent for Clinton and 18.9 percent for John Edwards. The late surge in the polls gives Obama's camp hope that Democratic-minded independents have only recently decided to support Obama over Clinton.

Crowd numbers also don't seem to be much of an indicator for Democrats. Obama has also seen large crowds, with one event on Saturday being attended by 2,500. Clinton held her own at the same location on Sunday. She has been trying to drive home the message that while Obama may be likable, he doesn't have the chops when it comes to foreign policy.

"I know that the next president will embody the hopes and dreams of all of us but I also know they can not be false hopes. We have to pick a president who will be ready on day one to do the job, the tough difficut job that will await," Clinton said.

Trying to fill the limited middle ground between Obama and Clinton, Edwards has argued that he has both the experience and the Washington outsider status to be an agent of change.

Asked, however, if he and Obama have an alliance to oust Clinton, Edwards said he is his own man.

"I want a debate -- listen, I like Senator Obama very much. We do have a basic general view that's very similar. But I have a very different view than he does about how we bring about change," Edwards told ABC on Sunday.

FOX News' Carl Cameron, Major Garrett, Wendell Goler and Caroline Shively contributed to this report.