COLUMBIA, S.C. — Racial politics, complaints and the Rev. Martin Luther King Jr.'s legacy dominated discourse in the Democratic presidential contest yesterday as Nevada caucus winner Hillary Rodham Clinton and Barack Obama sought to shore up their bases for the South Carolina primary on Saturday.

The new Republican presidential front-runner, John McCain, meanwhile, pivoted from his South Carolina victory to Florida's Jan. 29 primary, where he faces renewed combat with rivals Mike Huckabee and Mitt Romney and a test from Rudy Giuliani, who is trying to revive a deflated campaign.

The weekend results in Nevada and South Carolina firmed up the field in both parties as Clinton and McCain tried to portray their triumphs as evidence that they are in commanding positions. But the front-runners had no time to bask yesterday, wheeling quickly to face the next primaries.

Stung by his Nevada loss and by tense exchanges flaring between the two campaigns, Obama toughened his criticisms of the New York senator and her husband, former President Clinton.

Speaking last night to 3,500 supporters during a rally at the Metropolitan Convention Center in Columbia, Obama accused both Clintons of distorting his recent statement about President Reagan's ability to "tap into the discontent of the American people."

"When I see Sen. Clinton or President Clinton distort my words, say somehow that I was saying Republicans were the only ones who had good ideas since 1980, that is not a way to move the debate forward," Obama said.

Clinton spokesman Phil Singer responded that "we understand Sen. Obama is frustrated by his loss in Nevada, but facts are facts." Singer added that "President Clinton is a huge asset to our campaign and will continue talking to the American people."

Obama had told the Reno Gazette-Journal last week that "Reagan changed the trajectory of America in a way that Richard Nixon did not and in a way that Bill Clinton did not. He put us on a fundamentally different path because the country was ready for it."

"That's not the way I remember the last 10 to 15 years," Hillary Clinton replied. Her aides and surrogates elaborated with more detailed attacks on Obama, as did Nevada third-place finisher John Edwards.

Clinton and Obama spent yesterday in historic churches with black congregations, talking about race in America in advance of today's King holiday and a primary debate tonight in Myrtle Beach sponsored by the Congressional Black Caucus.

With the black vote in South Carolina and elsewhere coalescing around Obama, Clinton went to the Abyssinian Baptist Church in Harlem in New York City yesterday to firm up community support that has showed signs of hemorrhage despite backing from a long list of black political leaders. The New York senator won an endorsement from the Harlem church's influential pastor, the Rev. Calvin O. Butts.

In Atlanta, Obama sought to consolidate his support from southern black voters with an appearance in King's own pulpit at the Ebeneezer Baptist Church. In lofty cadences, the Illinois senator spoke glowingly of King's legacy, but also reminded his audience of his recent dust-up with Clinton and several of her surrogates over what he considers racially tinged criticisms.

As they turned their attention to South Carolina, several Clinton advisers and fundraisers tried to dampen expectations in that state, saying its large population of black Democratic regulars — nearly half the state's party voters — favors Obama.

One Clinton fundraiser said that bleak prospect came up at a recent dinner in Washington, D.C., with former President Clinton. The group discussed South Carolina, and the consensus was it would be tough to pull off a win, the fundraiser said.

McCain, whose GOP presidential campaign was in disarray last fall, savored his revival yesterday, taking aim at former New York Mayor Giuliani, who turned up on ABC's "This Week" attacking McCain for voting against President Bush's tax cut program.

Before flying from Charleston to Miami, the Arizona senator shrugged off Giuliani's critique while his aides noted that he had voted against Bush's tax cuts in 2001 and 2003 because they were not paired with spending reductions.

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

Giuliani is plying a risky political strategy, not contesting the early GOP primary states and making Florida a firewall where he hopes to woo non-native snowbirds, GOP moderates and foreign-policy conservatives as a winning coalition. Former Arkansas Gov. Huckabee and former Massachusetts Gov. Romney will compete among evangelicals and social conservatives.