Fresh off an invigorating win in South Carolina, John McCain called himself the front-runner in the Republican presidential race Sunday, and said while victory in Florida is important, it is not necessarily a must-win state.

He also took a shot at Rudy Giuliani, who has banked his political fortunes on a win in Florida, foregoing the early primary states in a daring strategy that has yet to pay off. Giuliani has seen his national lead shrink as he decided to concentrate on the Sunshine State while other candidates made headlines in earlier voting states.

Speaking in Charleston, S.C., before taking a day off ahead of his turn toward Florida, McCain acknowledged that the race is still competitive and that the candidates running against him for the GOP nomination are strong. But, he added, when the stress starts to build, as it has for Giuliani, it's no surprise for a candidate to go on the attack.

"When someone hasn’t won a primary, I can understand why they might attack the front-runner," McCain said.

Down in Florida, Giuliani appeared relaxed while waiting for his rivals' arrival. Voters go to the polls there, in both parties' contests, on Jan. 29.

"Florida is a microcosm of the country. It's a diverse state, reflects America," he said on ABC's "This Week." "It determined our president in 2000."

Giuliani once more noted McCain's opposition to President Bush's tax cut plans in 2001 and 2003, and argued that his executive experience makes him better suited for the top job.

"The case for me is that I am the strongest fiscal conservative," he added. 

Giuliani campaign manager Mike Duhaimie said despite the increasing number of barbs, McCain and Giuliani are long-time allies when it comes down to it.

"They are friends and there's a great deal of mutual respect among Mayor Giuliani and Senator McCain," Duhaimie told FOX News. "That's not to say they don't have differences."

McCain seemed unfazed by the back-and-forth as he looked toward Florida. Still reveling in the victory he was deprived of in the Palmetto State in 2000, the Arizona senator expressed confidence that he has the support of retirees and military veterans there as well as some Cuban-American members of Congress. The politically-active and connected Cuban-American voting bloc in Florida is large.

McCain, who has enjoyed the role of "maverick," a description he cultivated in the 2000 presidential race, said he likes being the underdog, but "I much more enjoy being ahead."

Elsewhere on the campaign Sunday, Mitt Romney, who won the Nevada caucuses a day earlier, portrayed himself as a Washington outsider compared to McCain, who Romney said has been "in Washington all his life."

"I just don't think that somebody who has spent their life inside Washington, who has lobbyists on every elbow ... I just don't think that's going to get Washington fixed," Romney said on "FOX News Sunday."

The former Massachusetts governor also spelled out his differences with the president on an economic stimulus plan proposed by Bush as a way to head off a recession. Romney he has a plan to fix the economy and "broken" Washington culture.

"Well, my system is primarily based on trying to create jobs, not handing out cash to individuals," he said. "I do lower the lowest income tax bracket from 10 to seven-and-a-half percent, and that helps, of course, people at the low economic level, but also for individuals 65 and older. The fact that they're not going to be paying Social Security or Medicare taxes anymore, no payroll taxes mean that that's going to be a break for them.

"But the heart of what I'm doing is trying to get businesses to become more active buying capital equipment, trying to get businesses to grow in this country, and to create more jobs. Because the best antidote to having economic slowdown is growth in the business sector, creating more jobs, putting more people to work and of course that generates more income for everybody," he said.

Mike Huckabee, who won Iowa and is looking for another victory to demonstrate he has broad-based appeal outside religious conservatives, was in Texas on Sunday, partying at the ranch of supporter and action movie icon Chuck Norris.

On the Democratic side, Hillary Clinton defeated rival Barack Obama in a tight Nevada contest. She claimed the Nevada popular vote as a victory though estimates show Obama edged her out of national convention delegates — 13 to 12, assuming delegates remain committed as they are now. 

Obama issued a statement that said he had conducted an "honest, uplifting campaign ... that appealed to people's hopes instead of their fears."

On Sunday, Clinton appeared in Harlem to pick up the endorsement of Rev. Calvin Butts III, pastor of Abyssinian Baptist Church. Butts introduced Clinton last week at an event by calling her "the next president of the United States," but only decided to endorse her officially a few days ago.

Butts said he had received calls from distraught admirers wondering how he could abandon a black candidate. He responded by saying, "Let me be clear: this was not a race-based decision."  Clinton herself praised Obama as a great person and said the two of them were both blessed to have strong, passionate spouses.

But outside the church, Clinton ran into some Obama supporters who yelled, "Don't come to Harlem to steal the black vote." On her way for coffee with some supporters, a group of Obama supporters chanted at her, "Be a part of something great, Obama '08." One of the half-dozen or so demonstrators yelled, "We don't want your coffee."

Much father South, the Illinois senator appeared Sunday in Atlanta at the famous Ebenezer Baptist Church, where he discussed racial division and the need for unity. Addressing a packed church and overflow crowd of hundreds who watched on the jumbo-tron outside the building, Obama said the U.S. suffers an "empathy deficit."

"Unity is the great need of the hour — the great need of this hour. Not because it sounds pleasant or because it makes us feel good, but because its the only way we can overcome the essential deficit that exists in this country," Obama said at the church where Martin Luther King served as pastor. 

"I'm not talking about a budget deficit. I'm not talking about a trade deficit. I'm not talking about a deficit of good ideas or new plans. I'm talking about a moral deficit. I'm talking about an empathy deficit. I'm talking about an inability to recognize ourselves in one another; to understand that we are our brother's keeper; we are our sister's keeper; that, in the words of Dr. King, we are all tied together in a single garment of destiny."

Back in South Carolina, where Democrats will vote in their primary on Jan. 26, John Edwards acknowledged a formidable loss in Nevada. He won 4 percent of delegates compared to Obama's 45 percent and Clinton's 51 percent.

"I got my butt kicked in Nevada," he said on CBS' "Face the Nation," where he vowed to go on. "I'm here in South Carolina, the place I was born, fighting with everything I've got."

Edwards also admitted he's the odd-man-out in a historic race that includes both an electable African-American and woman candidate.

"Of course it's a factor. There's no doubt about that.  And we've got a couple of candidates who have gotten massive publicity and raised $100 million plus each. But I'm not in the business of making excuses," he said. "All three of us are going to be perfectly fine when this thing is over. The question is, will we have done what needs to be done for America? ... I mean, that's what this is about.  It's not about any of us, personally."

FOX News' Jonathan Serrie, Bonney Kapp and Aaron Bruns and The Associated Press contributed to this report.