The best line I heard about Sarah Palin during the frenzied orgy of chauvinist condescension and gutter-crawling journalistic intrusion that greeted her nomination for vice-president a week ago came from a correspondent who knows a thing or two about Alaska.

“What's the difference between Sarah Palin and Barack Obama?”

“One is a well turned-out, good-looking, and let's be honest, pretty sexy piece of eye-candy.

“The other kills her own food.”

Now we know, thanks to her triumphant debut at the Republican convention on Wednesday, that Mrs Palin not only slaughters her prey. She impales its head on a stick and parades it around for her followers to jeer at. For half an hour she eviscerated Mr Obama in that hall and did it all without dropping her sweet schoolmarm smile, as if she were handing out chocolates at the end of a history lesson.

There's a powerful danger in the sheer thrill that has followed her astonishing performance that we could get carried away with John McCain's running-mate. Some of the coverage has a hyperbolic tone to it. Not since Paris handed that apple to Aphrodite has a man's selection of a woman had such implications for the future of our civilisation.

So let's stipulate one obvious and important piece of wisdom about US elections. The choice of a vice-presidential candidate rarely makes much of a difference. The pundit class waxes historical in the excitement of the moment but usually the vice-presidential choices go back to playing second banana. However mawkishly we dwell on the mortality of the presidential contenders, it is they who determine the voters' decision.

This one, to be fair, could be different. For at least the next few weeks the press will follow Mrs Palin's present and dig deeper into her past, still hoping for some morsel of stupidity or evidence of cupidity to doom her. But in the end, barring such a discovery, this is still an Obama-McCain contest.

But let me try to explain why Mrs Palin, whatever impact she might have in November, may be a figure of real consequence in our lives.

It's partly about what she represents and partly about what she has already done, but mostly about where she and her ilk might take the Republicans - and possibly America.

It never ceases to amaze me how the Left falls again and again into the old trap of underestimating politicians whom they don't understand. From Ronald Reagan and Margaret Thatcher to George Bush and Mrs Palin, they do it every time. Because these characters talk a bit funny and have ridiculously antiquated views about faith, family and nation, because they haven't spent time bending the knee to the intellectual metropolitan elites, they can't be taken seriously.

So the general expectation was that Mrs Palin would stumble on to the stage in high heels, clutching her sprawling, slightly odd family (five children! how weird), mispronounce the name of the Russian Prime Minister, mutter a few platitudes about God, and disappear for ever to a deafening chorus of sniggers.

No one paid much attention to the fact that she had been elected governor of a state. Or that she got to that office not because, unlike some politicians I could mention, her husband had been there before her, or because she bleated continuously about glass ceilings, but by challenging the entrenched interests in her own party and beating them. In almost two years as Governor she has cleaned out the Augean stables of Alaskan Government. You don't win a statewide election and enjoy approval ratings of more than 80 per cent without real political talent.

Never mind all that. She didn't have a passport! She was a former beauty queen! It was so axiomatic that she was a disaster that I was told by lots of savvy men - with deliciously unconscious sexism - that the real problem was what the choice said about Mr McCain and his judgment: cynical, irresponsible, clueless. It was as if Mrs Palin wasn't really a human being at all, but an article of Mr McCain's clothing that showed his poor taste, like wearing brown shoes with a charcoal suit.

So here's why she matters.

First of all she offers an opportunity for an ailing Republican party to reconnect with ordinary Americans. She's conservative, but her conservatism is not that of the intolerant, uncomprehending white male sort that has so hurt the party in recent years. She is much closer to a model of the lives of ordinary Americans - working mother, plainspoken everywoman juggling home and office - than any Republican leader in memory.

The contrast with Mr Obama is especially powerful. The very fact that Mrs Palin didn't go to elite schools but succeeded nonetheless - the very ordinariness with which she so piquantly jabbed Mr Obama on Wednesday - is what will make her so appealing to Americans. And as a pro-life conservative she debunks in one swoop the enduring myth that all women subscribe to the obligatory nostrums of radical feminism.

But there's more to it than that.

The Republicans have decided that they are not going to make the mistake Hillary Clinton made and run against the effervescent Mr Obama on the premise of experience.

Experience hasn't got Americans into a very comfortable place. They want change. Before he signed up to some of the less attractive Republican attitudes this year, Mr McCain's career had embodied that change - the anti-establishment candidate running against his own party. Now he is joined by a woman who, in her short career, has done the same thing.

Democrats think that Mr McCain, with the social conservative Mrs Palin, will launch an old-fashioned culture war at them, using her appealing manner to drive a populist assault on the familiar Republican issues of God, guns and gays.

Perhaps this Manichean interpretation will prove true. But I suspect that it misses the real appeal of the Republican team. The opportunity for McCain-Palin is not reaction, but reform - a reform rooted in a distant conservatism that could be due for a comeback

Hailing from Arizona and Alaska, the Republican ticket has a chance to rekindle a western conservatism different from the old Yankee paternalist sort or the Bible Belt version. They like their guns out there (some still kill their own food) and they are pro-life and deeply pro-America, of course. But at a time of grave challenges, the themes of economic freedom and opportunity, the resistance to the idea that government holds all the answers, could resonate with voters.

This is an election, as the Democrats have realised all along, about an America on the cusp of change. With the moose-hunting, establishment-taunting Mrs Palin at his side, Mr McCain might represent a bigger change than the one that his opponents are offering.

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