It is hard, sometimes, to remember that I don't have a vote in the US election. The media coverage is constant, my Twitter feed is full of it, and it is all that the blogs I read seem to be interested in - even the non-political ones. While Peter Mandelson is being brought into British government for the third time, the US political scene seems to dazzle with its array of new faces and new personalities. Barack Obama's inspirational idealism and John McCain's time spent as a prisoner of war make our politicians look a little grey and ordinary. And then there's Sarah Palin, who can see Russia from her house.

I am someone who really would like to see more women in government, but Palin makes me cringe every time I hear about her. Dan Quayle's repeated gaffes - and who can forget his gnomic remarks and inability to spell potato? - simply made many think that he was an intellectual lightweight. But it's hard not to worry that some people might see Palin's mistakes as a reflection on the intelligence of women in general. From her rambling and incomprehensible answers to simple questions, to her inability to define the Bush doctrine, to her apparent unwillingness to name a single newspaper she reads, her performance seems constantly to support the charge that she is simply not ready to become vice-president of the US. Interestingly, Jed Lewison, writing in the Huffington Post on October 1, dug up footage of Palin performing in debates on Alaskan issues in which she acquitted herself well, suggesting that she might simply have been brought up through the party ranks too quickly rather than that she's entirely incompetent.

And although I'd rather see a hard-hitting intellectual woman on either ticket, it has to be said that Palin hasn't sunk McCain's campaign.

Of course it's hard for British people to understand why anyone would vote for McCain/Palin. Our political consensus is to the left even of the Democratic Party. For example, even Obama isn't suggesting that the US bring in socialised medicine on the scale of the NHS. But for many centrist voters in America, the desire to vote in more leftwing leaders may be outweighed by other considerations. On a recent visit to the US, I met one or two of that rare breed of American voter whose existence I had previously considered merely a myth: centrists who want to elect a woman candidate, would have voted for Hillary Clinton if she'd been running, but are now intending to vote Republican because Palin is on the ticket.

What is this about? One explanation is the classic "ice-cream vendors on a beach" model of the two-party system taught to first-year politics undergraduates. This model, first conceived by Harold Hotelling and later developed by Anthony Downs, explains why political parties tend to move closer to one another. Imagine a long stretch of beach, with people evenly distributed along its length. Two ice-cream vendors set up their carts on the beach, one at the exact midpoint of the right-hand side of the beach, the other at the exact midpoint of the left-hand side. They both attract all the customers who are closer to them than to the other vendor; 50% each of the market. But if one vendor moves closer to the middle of the beach, they keep the customers at the extreme end of the beach, but also gain a few of the "centrist" customers. In order to gain back the lost ground, the other vendor also has to move toward the middle of the beach.

Applying this model to politics suggests that in a two-party system political parties will tend to move closer together over time, both ending up near the median point of voter sympathies. In practice, this would mean that, over time, there is less and less to choose between the political parties. If their policies are often practically identical, the only thing to choose between the candidates may be their religion, ethnicity, gender or sexuality. This would lead to an increasing emphasis on identity politics.

But, although the UK may have been getting closer to an equilibrium of this sort over the past 15 years, the US certainly isn't there. On the Iraq war, taxes, healthcare and the environment, McCain and Obama have made their policy differences clear; it's hard to imagine that anyone would feel they were too close together to decide between.

Another possible explanation of the increasing importance of identity politics that occurs to me is the decline of trust in politicians. In a survey carried out in 1964, about 75% of Americans said that they trusted the federal government. More recently, surveys have shown that around 75% of Americans now do not trust their government. Perhaps people were simply too naive 40 years ago, or perhaps we're too cynical now. One conclusion is clear to me, though: if you can't trust politicians to keep their promises, then policy statements lose some of their force to motivate the voter. If you believe that politicians will simply break their election promises, then what's left as a rational way to choose between them?

The rationale goes that, if elected, a McCain/Palin ticket might or might not actually follow through on any of their policies, but Palin will still - in all probability - remain a woman. For those who feel it would be an important breakthrough to have a woman in the office of vice-president, this is one campaign commitment she can hardly help but keep.

This week Naomi watched the Tom Hanks film Charlie Wilson's War for the second time: "It impresses even more second time around; intelligent, thoughtful film-making with much to say about the current state of the world." She ate apples and honey in celebration of Jewish New Year and worried impotently about the plight of the bees.