So, barring political earthquakes in the next three months - a phenomenon that we should by no means rule out - this year's presidential election on 4 November will not be as different as we once thought it might be. The choice facing the nation when it goes to the polls to pick its 44th president will be between two men in suits and ties, just as it has always been since the tradition was established 220 years ago.

Do not be misled by all the romanticised buzz about youth and change, either: if Senator Barack Obama moves into the White House on 20 January he will be less than three years from his sixth decade, older than (say) Bill Clinton was when he became the last Democratic president in 1993. If it is John McCain who triumphs in November, he will be fewer than eight years from his ninth decade - the oldest man to become US president.

In other ways, it will be business much as usual: each man went to elite private high schools, Obama proceeding further down the path of private education all the way to the Ivy Leagues, while McCain followed family tradition and joined the highly exclusive US Naval Academy. Each man has a background that certainly deviates from the historical norm, however. McCain, for example, was born in Panama - an overseas birth that theoretically disqualifies him from becoming president under the US constitution but is overlooked because he was born in a US naval facility. Uniquely for a US presidential candidate, Obama's upbringing and adolescence were spent outside mainland America, four years of it abroad; the young McCain, as the son and grandson of four-star naval admirals, spent many school holidays overseas at different US bases around the world, too.

Assuming the two men are formally ratified as the Democratic and Republican Party nominees at the end of August and beginning of September respectively, the battle that follows will be just as enthralling a roller coaster as the five months of the primary season have been. Either candidacy could implode instantly as the result of a gaffe or some unguarded moment: Obama's because of his potentially explosive blend of personal arrogance and political inexperience, McCain's because of his political erraticism, limited stamina and notorious hot temper. The sparks, we can be sure, will fly.

I will return to these potentially exciting scenarios shortly. Before that, however, let me re-emphasise something the US media found impossible even to countenance as the results of the last two 2008 primaries in South Dakota and Montana were coming in on Tuesday night (fittingly, Obama won Montana and Clinton took South Dakota by almost identical margins, by the way): that the democratic process in selecting the Democratic Party nominee, following the party's rules and procedures, is far from over and won't actually conclude until 28 August.

A pensive Hillary Clinton after the result. What will she do next?

Yet the gleeful, mounting expectation among the US punditocracy last Tuesday that Hillary Clinton would gracefully concede to Obama, obediently pack up her bags and hand the battle over to the big boys was stupendous to behold. MSNBC's über-commentator Keith Olbermann said perfectly seriously that this presumptuous female had tried to "shoehorn" her way to the Democratic nomination. There was universal dismay that Clinton did not shush her supporters when they chanted "Denver! Denver! Denver!" as she spoke in New York on Tuesday night, an unmistakable exhortation that she should continue the fight all the way to the Pepsi Centre convention floor in Denver in August.

I do not know (and I don't believe Clinton knows herself, at least not as I write this in the early hours of Wednesday) whether she will accept the vice-presidential nomination. She and Obama certainly loathe each other, but there is a long tradition in US politics of presidential candidates and their running mates regarding each other with contempt (for example, JFK and LBJ). I previously suggested in these pages that the denouement of this year's epic Obama-Clinton battle could come when planeloads of Obama lawyers and Clinton lawyers fly in to Denver to fight over the legal intricacies of the nominating procedures. That remains a long-shot scenario, but one that is still not inconceivable.

The reasons should be obvious even to the complacent US punditocracy, but they are not. If this five-month season of primaries and caucuses has taught us anything, it is that the absurd, outdated and ludicrously complex and contradictory procedures that govern US elections badly need to be updated and rationalised. (British enthusiasts who want to introduce UK primaries: please listen to me on this.)

It is simply outrageous, for example, that the validity of millions of votes cast in Michigan and Florida should remain in legal limbo merely because there are so many senseless rules and traditions. There is no good reason in the world, to give another, why the first caucus and primary contests of every presidential campaign must be in Iowa and New Hampshire, respectively, rather than in, say, Florida or Michigan. Hillary Clinton may have trounced Obama by a staggering 68-32 landslide in the Democratic primary in Puerto Rico on 1 June, but even though the island's four million residents are US citizens, they will be denied the right to vote in the 4 November election. So why should Puerto Ricans help choose the candidates in primaries, but then not be allowed to vote for any of them in November? Nobody seems to know; that's just how it is.

Countless anomalies of this kind do not normally matter, but when the race is extremely close - as it was when poor Al Gore won the popular vote for the US presidency in 2000 but then, under the arcane electoral college system and nudged along a bit by the Supreme Court, found George W Bush heading for the White House instead - they can actually end up being phenomenally destructive. The 2000 presidential election was close to being a dead heat, but Bush took advantage of the electoral anomalies to thwart the wishes of the majority of Americans who had voted for Gore to be their president.

The outcome of the 2008 Democratic primary season is remarkably similar: in effect it is a dead heat, too, although just as George W Bush legi timately garnered more electoral college seats under that antiquated system in 2000, so Obama has legitimately won more delegates under the impenetrably complex Democratic primary procedures this year.

Powerfully persuasive

Yet, just about whatever way you calculate the figures now, it is clear that more Americans actually cast their vote for Hillary Clinton to be the Democratic nominee than for Obama. She, poor woman, is the Al Gore of 2008. Had the Democrats run their primaries and caucuses in the same way as the Republicans, to give another example of the contrariness of the system, Clinton would have wrapped up the nomination long ago.

That, first, helps explain why she did not immediately curtsy to Obama and concede defeat in the humiliatingly defeatist manner so many were eagerly awaiting last Tuesday night. Bush, had Gore made it to the White House instead of him in 2000, would doubtless have suffered the same bitterness and resentment over being cheated of the presidency that subsequently afflicted Gore. In much the same way, both Obama and Clinton have every right to feel that they have emerged from the 2008 primary season as the people's choice for the Democratic nomination.

In American sporting parlance, Clinton had a terrible second quarter in which she ceded 13 successive victories to Obama in a losing streak that began on Super Tuesday (5 February) and ended in Vermont a month later. But her other three quarters have been strong, and she roared to recent landslide victories in West Virginia, Kentucky and Puerto Rico. She beat Obama in six of the nation's giant seven states, such as California, New York and Texas, and in a majority of other battleground states that could be decisive in November. No presidential candidate in history has ever lost six of the country's seven largest states in the primaries, as Obama has done, and gone on to win the White House.

That brings us to the second main reason why Clinton has not dutifully slunk away: she and her husband can still make powerfully persuasive arguments to the 789 super-delegates that she has a better chance of beating McCain in November than Obama. Even after the final primaries were over on 3 June, and weeks after the media had anointed Obama as the nominee, polls still showed that Clinton would beat McCain in November more easily than Obama. The super-delegates are leaning strongly to Obama and there may well now be an unstoppable exodus to him - but there is nothing to stop them changing their minds until the die is finally cast in Denver on 28 August.

If Clinton does not concede or accept the vice-presidential nomination, or decide the battle is lost, we can thus be certain that the Clinton camp will keep pounding away in private at the super-delegates about why she would be the better candidate until the very last moment on 28 August - simultaneously keeping their fingers crossed that good fortune, in the form of a major Obama gaffe or the exposure of a hitherto unrevealed skeleton in his cupboard, will swing their way.

The latest gossip, for example - and this is not from the Clinton camp - is that the McCain campaign has got hold of dynamite video footage of Obama's wife, Michelle, derisively dismissing "whitey" alongside Louis Farrakhan, the notoriously anti-Semitic leader of the Nation of Islam, at Obama's former so-called "buppie" church in Chicago (from which he chose to resign, in cidentally, only last Sunday). Heaven knows whether this rumour is true, but its very existence is indicative of the political volatility we can expect for the next six months. McCain is no racist, but (assuming Obama is his opponent) he is a former military boxer who will not pull his punches in the way that Clinton, as a fellow Democrat obliged to preach party unity, has felt she must do.

Yet things may well turn very ugly when the Republicans march into battle. The evil admen who managed to transform John Kerry's public image in a matter of days in the 2004 campaign from a genuine Vietnam War hero into an effete, French-speaking windsurfer will have nil compunction in trying to destroy Obama, too. Obama will constantly have to keep his hubris in check, McCain his temper. The dramas of this election year, I can assure you, are far from over.