Only one thing for the Democrats was clear: there will be no rest for either candidate in a competition awash with historic possibilities. Mr Obama could credibly claim that his chances of becoming the nominee and possibly the first African-American president were marginally improved. But Mrs Clinton's dream of rising to become the first female commander-in-chief remained more than alive.

By contrast, Republicans sensed relief as the confusion of recent weeks suddenly lifted to reveal John McCain – while still not quite across the finishing line – as the suddenly unassailable candidate. Mike Huckabee scored better than expected with victories across the South. Mitt Romney was largely eviscerated, his viability to go forward thrown into question. Count McCain as the candidate.

Now it is the Democrats who face muddle and strife. No correct calculus existed for measuring who made the most headway on Tuesday. Mr Obama captured the greatest number of states, winning 13 states to Mrs Clinton's eight, but his strategy of taking the key battleground states, especially California and Massachusetts, had notably failed. Female and Latino voters proved more resistant to the "Obama effect" than his campaign had hoped, turning out for Mrs Clinton in big numbers.

The race is now decidedly for convention delegates rather than states, but agreement was elusive even on who won the larger number of those in Tuesday's vote. The Obama camp, backed by some analysts, said he took more, partly thanks to the proportional system of awarding them. The Clinton camp averred. But in the game of expectations, at least, Mr Obama had done better in delegate terms than his aides had dared to predict going into Tuesday.

In any event, it remains a gargantuan struggle that will now extend much further down the calendar of primaries still ahead, beginning on Saturday with Louisiana – Mr Obama campaigns in New Orleans today - Nebraska and Washington state. On Tuesday, Democrats will vote in Virginia, Washington DC and Maryland. The clashes on 4 March in Ohio and Texas will be critical.

His campaign is playing down expectations, but in the next seven contests Mr Obama is strongly favoured. In four of them – Louisiana, Maryland and Virginia as well as the District of Columbia – there are large black populations and on Super Tuesday, he won extraordinary support from black voters; more than 80 per cent in New Jersey and Georgia. But he was also supported by white male voters and added major victories in mainly white states such as Idaho and Utah, even beating Mrs Clinton among white voters in California.

The Republican opposition will be worried about his scores in states marked "red" on the map rather than Democratic blue in recent elections. Mr Obama won a broad band of the Midwest, including Utah, Colorado, Kansas and Missouri. Yet his worse-than-expected showing in California and New York augurs well for Mrs Clinton. If neither candidate breaks free soon, the party will have reason to fret. While the Republicans have coalesced finally around John McCain, an extended battle between Mr Obama and Mrs Clinton risks draining money and turning sour.

With a lioness smile and citrus trouser-suit, Mrs Clinton strode on to the stage in midtown Manhattan on Tuesday night to deliver a speech to supporters that was flawlessly competent and oddly flat. Only a Clinton would talk about stem-cell research on Super Tuesday night. Was there any sign of let-down in the hall? Only if you count the giant disco ball in the rafters that refused to revolve.

Both campaigns know things could have gone differently. Had Mr Obama captured California or Massachusetts, the flow would have been much stronger in his favour. But if there were corners of disappointment in his heart, he was not showing it either.

When he appeared before supporters in a Chicago ballroom in the early hours of yesterday, his wife, Michelle, beside him in a dazzling red dress, the crowd went delirious. However contrived by his image-makers, there was a presidential aura about him as he took the stage. Addressing still-wavering voters, he said: "Change will not come if we wait for some other person or if we wait for some other time. We are the ones we've been waiting for. We are the change that we seek."

Mrs Clinton's officials acknowledged that the advantage in the near term, at least, may be with Mr Obama. Momentum and time are on his side, and now money too: he has a larger war chest than Mrs Clinton, with more than $1m (£500,000) pouring in every day.

Meanwhile, confirmation that Senator McCain will be leading the Republicans in the November election may also change the landscape. Most polls suggest that in match-ups with Mr McCain, the Illinois senator would defeat him but that Mrs Clinton, still a polarising figure in the country, might lose. Will Mr Obama be stressing this in days and weeks ahead? Of course he will.

And add in the enthusiasm of Mr Obama's army. Mrs Clinton has a wide base, including older Democrats, women and blue-collar families. But in Mr Obama she is facing something daunting: a movement. And so far, as he said, it has kept on swelling.

On Tuesday, Mrs Clinton successfully stopped that tide from becoming a deluge. But, if it is only a finger she has put in the dam, the former first lady could yet find herself swamped.

David Usborne in New York and Leonard Doyle in Chicago