A Photoshopped picture of Sarah Palin has been doing the rounds for the past few days; it shows her in a stars and stripes bikini toting a rifle - patriotism, hunting and cheesecake all combined in one image. Two minutes of Googling reveals that the rifle has been identified by gun nuts in Republican chatrooms as a Crossman pump pellet gun. Soft porn for rednecks. Expect to see it pinned to the wall in every gas station in Texas and tacked to the dashboard of every long-haul truck. But this cartoon-like depiction of her smothers what we need to understand about why Palin appeals to American voters and why American elections have been so deadlocked for the past decade, as if there were two Americas, doomed to lived on the same landmass under the same government, like hopelessly incompatible spouses.

A new novel, American Wife by Curtis Sittenfeld, published in the US this week, tells a fictionalised and thinly veiled story of Laura Bush, from small-town girl in the 1950s midwest to school librarian to Republican bride to President's wife. What you learn from the novel is that, like it or not, the American heartland is not so much a political ideology but an actual place with people living in it. Small-town Americans have values and a lot of those values are good ones: neighbourliness, family life, a knowledge of the land and what grows in it. The other America they see on TV seems without ethics - crime, violence, drug addiction, pornography and prostitution - and they don't want any part of it.

So clear is the divide between big-city and small-town America that one American friend said to me: "These whitebread Republicans are like children - someone has to tell them what to do and what to think, they're incapable of independent ideas."

The conviction by the left that the right is stupid is one of the defining and least attractive characteristics of contemporary politics. Assuming that anyone who disagrees with you is too dim to get your point is not itself a particularly brainy way to win others over to the essential correctness of your views. But it is true that to small-town Republicans the world is not a complicated place, because they have seen so little of it.

I asked a sophisticated and well-travelled Republican why he voted the way he did. He described growing up "dirt poor" in a small town in Northern California where joining the military was your sole ticket out; where the people in his family who depended on welfare stayed where they were and the ones who worked their fingers to the bone managed to make a better life for themselves. For him, joining the army led directly to an education. In fact, it led all the way to Princeton. But how, I asked him, baffled, could someone as intelligent as he is believe that George W Bush was anything but a cretin?

Because, he explained, people in small towns don't like or trust intellectuals, particularly ones who appear to be sneering at them for their supposed stupidity. They admire a plain-speaking man; it's what they know and what they are used to.

They always assumed Bush was a regular guy who could keep his thoughts concise.

So America is stuck. Two countries, mutually irreconcilable, who never meet each other and don't want to, either. Who distrust each other at best, despise each other at worst. And who have absolutely no understanding of the other.

Reading Sittenfeld's thinly disguised account of Laura Bush and her upbringing, it was possible to see that the modest lives of her midwestern characters both had dignity and made sense. But I only have to meet them in a novel, which I can snap shut as soon as I've finished it. Were I an East Coast Democrat, which is the only kind of American I can ever imagine being, I would have no objection to small-town Republicans - to their church-going and their hunting rifles and their flag-decked porches and their meatloaf with gravy, and their lemon chiffon cake. I could admire their intimacy with the wide prairie and the vast sky.

The problem is that when they're running the whole country, they want to take away abortion rights, drill for oil in Alaska (a Palin policy), ignore climate change, and start unwinnable wars. With the small-town Republican mindset in charge, the rest of America and the rest of the world is forced to live by small-town values, which aren't much help when you're trying to decide what, if anything, can be done about Iranian nuclear ambitions or more humbly, workplace date rape.

Can America survive another photo-finish election which the Republicans win, or will it be out and out war between the red and the blue states? Perhaps only small-town America itself can prevent it, such as the dental nurse who asked how the mother of five kids, one with Down's syndrome, could hold down a full-time job, one step from running the United States. Sarah Palin, bad mom. That might finish her.

· This week Linda witnessed the end of the months-long Desperate Housewives drought when it at last returned to Channel 4 on Wednesday: "I survived in the meantime with the theme tune as my mobile-phone ringtone." She finally saw, almost a year after everyone else, The Band's Visit: "A film that quietly rejoices in the absurdity of human nature."