But the beauty of the Unknown Quantity — at least as candidate, if not as president — is that he not only articulates the powerful desire for change ever present in democratic politics. He can, simply by virtue of being unknown, actually symbolise it. Senator Obama’s elegantly written manifesto is called The Audacity of Hope, and there’s an irony to the title. It is indeed audacious to think that hope — and not much else — is sufficient to run a great country.

Countering the appeal of the new in the nation of the reborn is never easy. Opponents tout their long experience as evidence of higher suitability for office and sometimes it works — for Lyndon Johnson in 1964, Richard Nixon in 1968, and George H. W. Bush in 1988. But like second marriages, American elections more often seem to represent the triumph of hope over experience, as Hillary Clinton, to her disastrous cost, discovered this year.

At first glance, then, the general election campaign that finally got under way in June after the long Democratic primary, might look almost like a parody of this recent history of American presidential politics. In the blue corner, up there on the sunlit uplands, is the new and youthful Mr Obama , who first came to national prominence just four years ago with an oratorical flourish at the 2004 Democratic National Convention, and who began campaigning for president when he had served less than one year in the Senate. In the red corner, where the day’s long shadows are accentuated by the gentle slant of media bias, is Senator John McCain, of Arizona,the man bidding to be the oldest-ever elected president, a man whose public life began in 1968 when he was shot down over Vietnam, and who has been a national figure — famous prisoner of war, congressman, senator, presidential candidate — ever since.

If the candidates match the stereotype, the parties they represent fit it even better. The Republicans look like a tired party, worn out by experience, rather than armed by it.