McCain, 71, now emerges as a front-runner in Florida and the Feb. 5 so-called Super Tuesday contests in more than 20 states. Former New York Mayor Rudy Giuliani, 63, who has yet to win in a primary or caucus, is counting on Florida to give him his first victory.

Giuliani now "really needs to win Florida to demonstrate he remains a serious and credible contender," said Whit Ayres, a Republican pollster not aligned with any candidate.

For McCain, the strong showing in South Carolina "provides a measure of sweet justice," after his loss in 2000, Ayres said. That year, he was the target of a rumor campaign that sought to turn the state's Republicans against him.

Soon after McCain declared victory, his campaign sent an e- mail seeking donations for Florida and later contests. "Now that John McCain has won both the New Hampshire and South Carolina primaries, he has passed the historical test for Republican candidates and is on course to win," it said.

McCain's showing in South Carolina "is a huge springboard for him," said Tony Fabrizio, a Republican pollster who isn't aligned with any campaign. Placing second "certainly keeps Huckabee alive, particularly in Florida," he said.

Failing to place in the top two in South Carolina means Thompson, 65, isn't likely to get traction elsewhere, Fabrizio said. "He might as well go back to living the easy life," he said of the former actor.

Rep. Duncan Hunter, a California lawmaker, dropped out of the presidential race. He took less than one percent of the vote in South Carolina. "Today, we end this campaign," Hunter said in a statement on his Web site.

Florida is a winner-take-all primary with 57 delegates. The Real Clear Politics average of the latest polls for Florida shows McCain leading with 23 percent of support, followed by Giuliani with 20 percent. Romney is third with 18 percent.

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Contributing: Ed Chen in Columbia, S.C.