South Carolina’s primary would enjoy even more stature this time around. After the '04 trial run, the Democratic National Committee, in a nod to the importance of black voters, decided to make the state's primary one of four officially sanctioned lead-off contests in 2008. It would bat clean-up, at the end of January, after Iowa, New Hampshire and caucuses in Nevada.

On the night of Jan. 3, Obama won the Iowa caucuses, drawing strong support from young voters and those angered by Clinton's Senate vote to authorize the Iraq war. In a further surprise, Clinton finished third, edged out by John Edwards, the former senator from North Carolina and vice presidential nominee four years earlier. All of a sudden, it seemed, Obama was in position to deliver an early — and stunning — knockout blow if he could just defeat Clinton in New Hampshire. Polls immediately after Iowa showed him running away with the race, but Clinton capitalized on a last-minute Obama misstep and engineered an upset win of her own in the Granite State, which she followed up with a victory in Nevada.

Now it was up to South Carolina and a Democratic electorate that figured to be at least 50 percent African American. Clinton had righted her ship and now had her own opportunity to pull away from Obama. A win in the state, or at least a competitive showing with black voters, would set her up well for upcoming contests in other states with large black populations.

But as Obama had predicted, his victory in Iowa altered the contours of the South Carolina campaign. After trailing Clinton in state polls throughout '07, Obama was now running ahead. Previously hesitant black voters appeared to be coming around.

This seemed to irritate Bill Clinton, who had begun taking swipes at Obama. In one interview, he called the Obama candidacy "a roll of the dice." In another, he branded Obama's early opposition to the invasion of Iraq "a fairy tale." Then, with Obama gaining ground, Clinton tried pre-emptively to diminish the significance of an Obama win in South Carolina, saying: "Jesse Jackson won South Carolina in '84 and '88. Jackson ran a good campaign. And Obama ran a good campaign here.” (“Obama is Big Winner in S.C.," Dan Balz, Anne E. Kornblut and Shailagh Murray, The Washington Post, Jan. 27, 2008.)

The former president's posture provoked a public dressing down from Rep. James Clyburn, the state’s sole black congressman, who told Clinton to "chill it.” (“Focus shifts from Hillary to Bill in South Carolina,” The Guardian, Jan. 22, 2008.) A decade earlier, author Toni Morrison had dubbed Clinton "our first black president." Now, invoking that famous line, Clyburn remarked: "We are still looking for the first black president." (“Sharp attacks for both sides,” Glenn Thrush, Newsday, Jan. 25, 2008.) Officially, Clyburn was neutral, but his message was clear.

Hillary Clinton herself stirred up racial sensitivities in an effort to portray Obama as a skilled orator with little ability to produce results. To make the point, she drew an analogy to the civil rights movement. For all of Martin Luther King Jr.'s eloquence in pushing for an end to segregation, she said, "it took a president" — Lyndon Johnson, a white man — "to get it done." The ensuing controversy left Clinton trying to justify the remark just as South Carolinians made up their minds. "She, I think, offended some folks who felt that somehow diminished King’s role in bringing about the Civil Rights Act," Obama said. (“Clinton’s King Comment ‘Ill-Advised,’ Obama Says,” Anne E. Kornblut and Perry Bacon Jr., The Washington Post, Jan. 14, 2008.)

By primary day, Obama was expected to win, but his final margin was still jarring in its scope: 55 percent of the vote, nearly 30 points better than Clinton, and a near-sweep of the state’s counties. In victory, Obama won a quarter of the white vote, with Clinton and Edwards — a native South Carolinian — taking the rest. But it was African Americans who gave Obama his landslide. Enthusiasm among black voters was staggering; they made up 55 percent of the primary electorate, with Obama claiming 78 percent of their votes, according to NBC News’ black voter data analysis.

The drama in South Carolina had lingering effects. Just months earlier, it had seemed plausible that Clinton would outperform Obama with black voters. Now, though, Obama's African American support skyrocketed everywhere. Endorsements poured in from black leaders who'd been on the fence, or even in Clinton's camp. Lewis withdrew his support of Clinton and signed on with Obama. "I want to be on the side of the people," he explained. (“John Lewis Changes Endorsement to Obama,” Jeff Zeleny, The New York Times, Feb. 28, 2008.)

The calculations of white Democratic leaders were changed by South Carolina — and by the Clintons' behavior. Offended in particular by Bill Clinton's politicking, Sen. Ted Kennedy of Massachusetts endorsed Obama after South Carolina.

The campaign didn't end in South Carolina, though. Instead, clear demographic divisions developed and then deepened. Obama began rolling up well over 80 percent of the black vote and combining it with strong support from young voters and college-educated white liberals. Clinton, meanwhile, did well with Latinos and, as the race unfolded, better and better with white voters without college degrees.

Campaign trail flare-ups only reinforced these new coalitions. Scrutiny over the blistering rhetoric of Obama's pastor, Jeremiah Wright, boosted Clinton’s standing with blue-collar whites, even as Obama's response — a lengthy oration on the subject of race — strengthened his own base's loyalty to him.

Each candidate’s bandwagon was big enough to win millions of votes, hundreds of delegates and numerous states, but neither's was big enough to decisively put the race away.