It’s fair to say that Hillary Clinton has been planning her presidential campaign from the moment her husband left office, if not long before. And Rudi Giuliani has always thought himself presidential material, a view shared by some New York Republicans, and a few Democrats outside Manhattan, and not many others. But the theatre politics would be far less compelling, even were Mr Giuliani’s role but a walk-on, walk-off bit part. The cast of interesting, unusual, determined and dysfunctional characters grows with each passing day. If the capacity to create excitement alone was enough to win a presidential nomination then Senator Barack Obama would have a splendid chance of not only being the Democratic standard-bearer but also in securing the White House. The official launch of his campaign in Illinois today will be an emotional occasion. Although the Senator is a calm individual, the desire of Democrat activists for a fresh figure has lent a frenzied atmosphere to the drive of this “outsider” to derail Senator Clinton’s “insider” bid for the Oval Office.

Mr Obama is, without doubt, a very appealing prospect. Although his capacities as a public speaker have been exaggerated, his personal history is compelling. He took the Democratic convention in 2004 by storm when he was chosen as the keynote speaker. Later that year he was elected almost effortlessly to the Senate. From that moment, he has been feted by those who want the Democrats to offer a politically correct message, especially in opposition to US policy in Iraq.

For that reason, Mr Obama’s quest is destined to begin against a benign back-drop. Mrs Clinton voted in favour of the Iraq conflict in 2002 and (to her credit) has not entirely reversed that stance even as it has become unpopular. She is plainly an able and organised politician but not an inspirational performer. Mr Obama could fill that charisma gap.

In most other respects, however, he is almost entirely unknown. Were he to be nominated he would be the least experienced contender for either of the main parties since Jimmy Carter, a one-term Governor of Georgia, was selected by the Democrats in 1976. Mr Carter’s improbable success would have been unthinkable without the Watergate scandal, and his was hardly an effective presidency. Experience counts, not only in the winning of an election but also in leadership afterwards. Translating the intense energy that surrounds Mr Obama into a coherent strategy for victory is a massive undertaking. It may well be that the Senator falters as he enters the actual election year, much as Howard Dean did spectacularly in 2004.

Whether he succeeds this time or not, Mr Obama’s presence is an indication of how America has changed. His race is a factor in his appeal to some voters yet he is not a “token” politician. There is little evidence that if he does not triumph it will be as a consequence of the colour of his skin. There is no bar to a black person occupying the White House. This was illustrated by the interest that Colin Powell sparked more than a decade ago when he contemplated seeking the Republican nomination. There are plenty of Republicans who are keen to see Condo-leezza Rice, the Secretary of State, chosen as their next vice-presidential candidate.

Whether it be the most senior positions in politics, national culture or sport (both of the Super Bowl coaches this year were African-Americans) the notion of the United States as a rigid and segregated society is one that deserves to be challenged. If nothing else (and there may be more besides), Mr Obama will surely do that. This in turn should prompt some of America’s many critics abroad to ask if their own societies are as meritocratic.