Rupert Cornwell: Instead of the coronation of Barack Obama, we witnessed the triumph of democracy

What happened? Even in this roller coaster US presidential campaign that admits of no pause, let us stop for a moment to wonder how on earth Hillary Clinton pulled out the win over Barack Obama in the New Hampshire primary that almost certainly saved her candidacy from collapse.

It wasn't only the polls and pundits – not to mention this newspaper – that were confounded. So too were the Clinton and Obama campaigns. Both were openly expecting an Obama victory. She was poised to shake up her team of advisers, and already pleading with all-important financial backers to keep the faith. He was a candidate transformed by his success in Iowa's caucuses a few days before, not so much a man as a movement, that would sweep all before for it.

"Something's happening," Obama would say, too confidently sensing a tidal wave of support that would sweep him all the way to the White House. Then came the juddering shock of Tuesday, of which neither anecdotal evidence nor the final polling gave the slightest forewarning. But the lesson is clear. In politics, if not in nature, tidal waves can be halted. But again, how?

I'm sure that the moment, shown again and again on TV, when the eyes of America's Iron Lady welled with tears, and her voice choked, had something to do with it. We knew she was tough, and fearsomely competent. But now the woman who never let her emotions show, had proved she was as human as the rest of us.

Maybe this in turn caused women voters, one of Hillary's core constituencies, to return to the fold, after their flirtation with Obama in Iowa. Undoubtedly, the powerful counter-attraction of the Republican John McCain to independents, who can vote in either primary in New Hampshire, also played a part. Had McCain not been fighting for his own political life, independents might have voted overwhelming for Obama, just as they did in Iowa.

But I see it in classic historical terms. An ornery and contrarian little state has again done its appointed job. The New Hampshire primary is so important because its voters take their role so seriously. They hate being told what to do, they hate being seen as predictable. Instead their collective judgement has sent a message for which America should be profoundly grateful.

In 1968, New Hampshire told Lyndon Johnson the game was up. In 1992 it awarded Bill Clinton a second-place finish, urging the rest of the country that for all his sins, the then Arkansas governor was worth another look. A third example was 2000. By giving McCain a massive upset primary victory over George W Bush, they gave the latter a taste of defeat – and sent America a warning. Don't blame New Hampshire that the country didn't listen.

This time the message is no less precious. By rescuing Hillary Clinton at the eleventh hour, New Hampshire has served notice that an Obama coronation – which a victory for the Illinois Senator would probably have guaranteed – would be as unhealthy for the US democratic process as the Clinton glide to victory that for most of last year seemed pre-ordained.

Barack Obama may yet win the nomination. His life story is inspiring. The hope and excitement he generates, not least among young people, is remarkable. So is his extraordinary appeal across traditional political divides, and his ability to make the country feel good about itself at a moment of extreme doubt and self-searching. All of the above remains true, unaffected by one very narrow loss (which the polls incidentally were exactly predicting, until Iowa rudely intervened), and Hillary Clinton cannot match them.

But all of the above has also meant Obama has been given kid-glove treatment by the media. To read about him in the past few days, he comes across as a mix of Martin Luther King, JFK and Mahatma Gandhi. If that's still not enough star power, throw in a dash of George Clooney for good measure.

But thanks to the absence of scrutiny, Obama is still a largely unknown quantity. Strip away the fuzzy feel-good rhetoric and the substance of what he says is pretty banal. Yes, as Hillary found out, experience and mastery of the issues are not everything. But the notion of someone with just three years on the national stage as a US senator (and not a very distinguished senator at that) being catapulted into the most important job in the world, no questions asked, was always as absurd as an effortless dynastic restoration, achieved by a woman whose main claim to fame was being married to Bill Clinton.

New Hampshire has made sure neither will happen. Yes, American presidential election campaigns go on for ever, and cost an obscene amount of money. But they are protracted and all-examining for a good reason – to provide the fullest possible audition of a candidate for a job for which no previous training can ever quite prepare him (or her).

Now, this confused and exhilarating campaign is even more confused and exhilarating than ever. On both sides, there is an embarrassment of riches, and also of possibilities. In Clinton and Obama, Democrats have two exceptionally strong candidates. And for all the grumbling at the Republican field, it too is pretty impressive.

We have a principled and independent-minded war hero in McCain, who was counted among the political dead until his own resounding victory in New Hampshire. There is a proven big city mayor (Rudolph Giuliani), a former successful state governor and businessman (Mitt Romney), and an engaging Christian conservative populist (Mike Huckabee) – to name just the four leading candidates. None of them is perfect. But each has a chance of winning the nomination. Whatever else, you can't complain of a lack of choice.

On the Democratic side, matters will probably be settled in the next four weeks, above all on 5 February when 22 states vote. But so scrambled is the Republican field that we may well be treated to the forgotten thrill of a brokered convention, when the party gathers in Minneapolis in early September with its choice of nominee still in doubt.

Predictions are impossible, but I'll make one nonetheless. There won't be a third-party candidate. The results in New Hampshire have scotched that possibility. The record turnouts there and in Iowa have shown that centrists and independents are engaged in the contest as never before.

In these circumstances, an independent candidate who entered the contest after the main primaries were over, would effectively be telling voters they'd been wasting their time. But what would the vastly wealthy Michael Bloomberg, Giuliani's successor as mayor of New York and the name most mentioned, add to a field already brimming with possibility? Having written that of course, and given what happened in New Hampshire, I've probably made sure that Bloomberg will enter the fray. 2008 is that sort of year.