A race that began as the West Wing now looks alarmingly like Desperate Housewives. Six months ago, you couldn't help but notice the striking similarity between Barack Obama and Matthew Santos, the fictional but charismatic ethnic minority candidate who promised to heal America's divide. Now, you can't help but feel you're watching an especially lurid episode from Wisteria Lane, as the real-life Sarah Palin fends off rumours of a fake pregnancy - and the accusation that her son is actually her grandson - by revealing that her unmarried 17-year-old daughter is expecting a baby and will soon marry the father, a young hockey player. Meanwhile, Palin has hired a lawyer to beat back a state investigation into claims that she abused the power of her office to remove her sister's ex-husband from his job as a state trooper, a man who has admitted tasering his own 10-year-old stepson! Would even America's trashiest daytime soaps dare squeeze that much action into just the first four days of a new storyline?

The McCain campaign has done it, thereby achieving in an instant one of its key objectives. At last people are talking about the Republicans, after months in which all the excitement had been on the other side. Ever since McCain introduced Palin to a stunned, unprepared political world last Friday, Obama has barely had a look-in. From conservative talk radio to celebrity gossip websites, there is only one topic: it's all Palin, all the time.

In these reams of commentary, there is uncertainty about the only question that really matters: how will this saga, and Palin herself, play in the November election? Ultimately, will she hurt or hinder John McCain?

If it's hard to tell, that's because almost every new nugget we discover about Governor Palin can be viewed in radically opposite lights. The "family values" brigade might be shocked by the admission of premarital sex in the Palin clan; or it might be heartened that young Bristol - even the names sound like they come from a TV soap - has chosen to carry her baby to term and marry the father. So far, the latter reaction seems to have prevailed, with the Christian right, already smitten by Palin's anti-abortion, pro-guns, anti-gay marriage stances, standing by its woman. Some McCain backers have even tried to turn the episode into a net positive: talkshow host Michael Graham wrote yesterday that Palin, with one son off to Iraq, another with Down's syndrome and now a daughter set to become a teenage mom, had undergone experiences that millions of American women could relate to: "Sarah Palin is as accessible as Obama is exotic."

Or take what was, until the soap suds started lathering up, Palin's most obvious weakness: her inexperience. To political veterans, it's ludicrous to propose that a 20-month governor of a state with a population of under 700,000 is ready to take over as president (not such a remote possibility, given that John McCain is 72 and has a history of cancer). They note that when Palin visited Kuwait last year, she reportedly had to apply for a passport: she had never travelled outside North America before. How could she possibly be ready to lead the world's greatest military power?

But Democrats who make these points risk doing the Republicans' work for them, falling into the wearily familiar trap of sounding like condescending coastal elitists, who look down their noses at ordinary Americans like the Palins. The blue-collar Republican base is already wild for the governor: every time they see a New York talking head say how absurd her candidacy is, they'll like her even more.

Besides, the McCain camp is already hard at work spinning that all this inexperience is a good thing. It means, they say, that Palin will be a "breath of fresh Alaska air" in stale Washington, an outsider who had already dared take on politics-as-usual in her own state. Viewed that way, Palin has restored to McCain what always used to be his USP: his status as the reformer, fearlessly standing against the machine.

So she will go into the vice-presidential TV debate against the seasoned senator and foreign policy sage Joe Biden cushioned by subterraneanly low expectations. If she manages to utter several coherent sentences in a row, it will be declared a draw. If he so much as looks patronising or if he does an Al Gore-style sigh of impatience, she will be declared the winner. He's a bruiser who would have been eager to crush any male opponent. Now he'll be holding himself back lest he looks like a sexist pig.

There are some straightforward negatives for Palin that are not susceptible to even the most energetic spin. It's not good that she turns out to have been for the notorious "bridge to nowhere" - a $400m project in Alaska that has come to symbolise wasteful, "pork-barrel" spending - before she was against it. It dents her image as a reformer and shows she flip-flops as much as any other politician. Not helpful, either, that in the 1990s she was a member of the Alaskan Independence party, which seeks a referendum on breaking away from the US. The firing of her brother-in-law, and the outstanding request that she give a deposition on the matter, under oath, will linger through the campaign. And the fact that the McCain camp seems to have started seriously vetting Palin after nominating her, only now sending lawyers and researchers to Alaska, reflects especially badly on McCain himself. (He met her properly for the first time last week, according to the New York Times.) It suggests the downside of all that maverick brio is a recklessness that is hardly suitable in a commander-in-chief.

What no one can know is whether that cost will be outweighed by the gains Palin brings, galvanising a socially conservative base that had been previously lukewarm towards McCain. What we can know already is that this election will share a depressing feature with the contests of the past 40 years: that America will plunge again into the never-ending culture wars.

For Palin cannot help but polarise the electorate. Everything that liberal, blue-state America can't stand about her makes conservative, red-state America swoon. It's not just about "Jesus babies and guns," as Rush Limbaugh pithily put it. Palin also wants "intelligent design" - creationism - taught in school. When she was mayor of the small town of Wasilla, "she asked the library how she could go about banning books," according to a local official quoted by Time. Palin was worried about "inappropriate" language. "The librarian was aghast" - and was later threatened with the sack.

In his stirring speech last week, Obama urged America not to "make a big election about small things". Yet here we are, discussing not Sarah Palin's record or programme but Jesus, guns, and as one feminist blogger put it yesterday, "the uterine activity of her family". This is a setback for women, especially in a year that seemed to promise a breakthrough, but it is also a setback for America itself.

Obama made his name four years ago with a speech that called for an end to the civil war of red against blue. In 2008, he urged a different kind of election, one that would match the gravity of the hour. But the naming of Sarah Palin, and the reaction it has provoked, has dashed that hope. Americans are, once again, fighting over the questions that politics can never really settle - faith, sexuality - and pushing aside the ones that it can. And which it must.

freedland@theguardian.com