On the eve of a Super Tuesday

It's around 5pm: I am walking down Market Street, the main thoroughfare that runs through the centre of downtown San Francisco, and I hear a crowd approaching. At first I think they are protestors, because of the shouting and placard waving. But I am wrong.

Numbering around 50, they carry homemade signs and placards bearing the name "Obama", and they are all chanting the same phrase, over and over: Yes We Can. The realisation they are shouting in praise rather than anger is strangely intoxicating in the fading light of this beautifully sunny evening.

Political energy is high in San Francisco tonight. Tomorrow is Super Tuesday, when supporters of America's two main parties in almost half of the country's states - including California - vote to choose their preferred candidates ahead of the presidential election proper later this year.

In this famously liberal city, the debates and ad campaigns are all focussing on the two remaining Democratic hopefuls: Hillary Clinton and Barack Obama.

I can't vote, but I have been intrigued by the contest, especially because of the passionate debates it has sparked among my friends. Which candidate is best qualified to lead the country? And, perhaps more importantly, who has the best chance of beating the Republicans?

Hillary has the weight of experience and an impressive political pedigree. But Obama offers a heady mixture of youth, excitement and charisma. Sure, few people same able to say how the two differ in terms of policy, but to nitpick over that is to kind of miss the point.

Obama is new, he is fresh and he is exciting. Is that enough to get him into the White House? Should that be enough? Probably no more than the fact that Hillary is a woman, or a Clinton.

Perhaps unfortunately the desire for change here reminds me a little of the wave of optimism that swept Tony Blair to government in the UK in 1997. And that's the thing about change: you can never be sure exactly what you're going to get. But you can hope.