US:The Clintons' campaign has revived the spectre of electing 'Billary', reports Denis Stauntonfrom Charleston
Barack Obama's resounding victory in South Carolina represents not only a crucial boost to his bid to become the Democratic presidential nominee but a sharp rebuke to Hillary Clinton and - more particularly - her husband.
Bill Clinton put himself at the front and centre of his wife's campaign in South Carolina, acting as her surrogate-in-chief at events throughout the state and apparently savouring the role of an attack dog as he poured scorn on Obama's credentials as a candidate.
The more Democratic bigwigs and the media complained about the former president's hardball tactics and racially charged language, the more he appeared to enjoy his return to the spotlight.
The Clinton campaign sought to give the impression that it had long written off South Carolina but it never expected a defeat as overwhelming as Saturday's, which saw Obama win twice as many votes as Clinton.
Hillary Clinton had the support of almost the entire Democratic establishment in the state, including most black political leaders, and employed some of South Carolina's most experienced political operatives.
Her supporters trumpeted the warm relationship both Clintons have long had with African-Americans, confident that the former president's campaigning would rally a substantial minority of black voters to her flag.
Instead, 80 per cent of African-Americans backed Obama, who also picked up one in four white voters.
Obama's victory was so emphatic and so broadly based that the Clinton campaign cannot plausibly dismiss it as an insignificant bump along the path of her progress to the nomination.
South Carolina has, as Obama declared on Saturday night, put a new wind at his back ahead of Super Tuesday on February 5th, when 22 states choose more than half of the delegates who will select the Democratic nominee.
Clinton expects to win Florida tomorrow but that state's delegates have been told that they will not be seated at the Democratic convention because, like Michigan, Florida defied the party leadership by holding an early primary.
While Clinton focuses on big, delegate-rich states such as California and New York that hold primaries on Super Tuesday, Obama is turning his attention to states such as Colorado and Minnesota that will hold caucuses.
Caucuses, which require voters to show up in person at an appointed hour, tend to be more rewarding for grass-roots campaigns like Obama's.
Both candidates - and John Edwards, who is determined to stay in the race as long as he can - will be competing everywhere, however, because the Democrats award delegates proportionately, allowing even the losing candidate to pick up delegates in each state. If the race for delegates remains close, Edwards could play a pivotal role in determining the outcome by urging delegates pledged to him to back either Obama or Clinton.
One-fifth of the delegates at the Democratic convention will be "super-delegates" - members of Congress and other party notables who can vote for whomever they choose. The super-delegates, who represent the party establishment, traditionally swing their support behind the front runner and most are unlikely to show their hand until the primary race becomes clearer.
Many leading figures within the party are uneasy about the style of Hillary Clinton's campaign in recent weeks, particularly her husband's aggressive attempts to undermine Obama's credibility. The racial overtones of some attacks on Obama could also serve to alienate African-Americans, a key Democratic constituency, if Clinton eventually wins the nomination.
Bill Clinton's elevated profile has also raised questions about his role if his wife becomes president, causing some commentators to revive talk of "Billary" and the idea of a co-presidency. As one of Hillary Clinton's closest advisers told me recently, her husband remains popular among Democrats but many baulk at the prospect of giving him a third term as president.
"There is a certain lack of enthusiasm for the restoration," he said.
Obama faces significant challenges too, however, notably in expanding his support among white voters - especially women - and winning over Latinos, who appear to be breaking overwhelmingly in Clinton's direction.
All three campaigns now believe that the race for the presidential nomination will now stretch well beyond Super Tuesday and could even be decided at a brokered party convention in August.
"This is going to come down to mathematics," Obama's chief strategist David Axelrod said this weekend.
"This isn't about spin, it's not about division, it's about addition - who can put together the number of delegates needed to win."