It will be an enormous pity if the results of Super Tuesday bring the Republican and Democrat races to a premature end, for this has been the most pulsating American election in 40 years.

In 1968, however, the US had been convulsed by the Vietnam War and urban riots and approached its choice of president that year in a fearful and divided spirit. The race was tinged by tragedy as first Martin Luther King and then Senator Robert Kennedy were murdered, the latter a few moments after he and his supporters had celebrated triumph in the California primary.

The distinguishing features of the 2008 struggle, by contrast, have been not merely the astonishing drama and spectacle but the optimism that the election has generated.

This is a very unusual political competition. It will not be repeated in the same fashion for many years, possibly decades, to come.

Three factors have come together to make for such an historically rare occasion.

The first is that both parties have enjoyed truly open battles. In every election since 1952 one or other party has nominated either the sitting president for a second term or an incumbent vice-president to succeed him and those individuals have proved virtually impossible to deny the nomination. Not only is there no such person on the ballot this year but, in contrast to 1952 and other moments that were similar, there is no one in the Republican battle who might be considered the “White House candidate”.

The last time an election produced two ultimate contenders who felt at liberty to disown the president of the day if they so wished was the 1896 contest. There is quite literally no living American who has had experience of an election akin to this.

Throw in that there might be the first female president or the first mixed-race one or the first Mormon or the oldest man to be elected for the first time to the Oval Office and the event is irresistible.

The second element involves a somewhat more recent American election. In 2006 the Democrats won back control of both the House of Representatives and the Senate. This had not happened in the sixth year of a presidency since Woodrow Wilson was humiliated in 1918. It signified that the Bush era was over and prompted thoughts to turn to his successor. This election has been running for the better part of 12 months already.

The third aspect was a significant change in the primary calendar. The larger states had traditionally voted in the late spring but found, to their immense irritation, that the nominations had been more or less settled by the moment that they participated. The influence exercised by the likes of Iowa and New Hampshire was resented.

The result was a stampede to vote earlier and the creation of a Super Tuesday in which more than 20 states would cast ballots. Bobby Kennedy’s victory in California four decades ago occurred in the first week of June — California’s support has been decided four months earlier this time.

Worried at being marginalised, the states that were used to being early in the frame organised their primaries even earlier. What has emerged is a tantalising timetable in which a small set of states — Iowa, New Hampshire, South Carolina and Florida — have served to narrow each party’s choice down to two realistic contenders.

It is perhaps ironic that this captivating political contest has taken place during the writers’ strike in Hollywood. Only a skilled master of fiction could have created a plot to resemble the epic standoff between Hillary Clinton and Barak Obama or John McCain’s return from oblivion. The script has been sensational. Let us hope that there are a few scenes left.

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