Hurricanes Gustav and Hanna may have brought hell to the people of America's Gulf Coast, but they came like manna from heaven for Senator John McCain, his brand-new running mate Sarah Palin, and the Republicans. First, McCain was quicker off the mark than Barack Obama by taking the decision to abandon political rallies, and he toured the affected areas instead - getting priceless footage on to the nation's television screens of a would-be president looking and acting just like a president should, receiving briefings and talking knowledgeably about the situation in press conferences and interviews. Obama, meanwhile, was stuck looking helpless in Lima, Ohio - 1,000km north.

Second, Hurricane Gustav made landfall in the early hours of 1 September, the day the Republican convention, destined to crown McCain and Palin, was due to begin in St Paul, Minnesota. You would have thought, four days after the Democratic convention in Denver reached a televised climax with Senator Obama's acceptance speech, fireworks and balloons at his $6m extravaganza in the Denver Broncos stad ium, that McCainites would have wanted every minute of live, coast-to-coast television they could get.

But a convention on Monday night would have been their nightmare: the scheduled speakers were none other than George W Bush and Dick Cheney - the last thing McCain would have wanted the nation to see was those two passing their mantle to him. Bush, mindful of his ineffable performance when Hurricane Katrina struck in 2005, stayed at the White House and immediately cancelled his appointment at the convention. So did Cheney, who was off - phew! - to Georgia, Ukraine and Azerbaijan the next day, making any appearance by him impossible.

Third, besides creating the illusion that he was taking charge of hurricane preparedness, McCain - emboldened, I suspect, by at last having a running mate of his own - seized the opportunity to make himself appear to be a thoroughly responsible decision-maker by selflessly cancelling the razzmatazz planned for Monday night. "This is a time when we have to do away with our party politics and we have to act as Americans," McCain said in an oh-so-respon sible broadcast that, had he been reading more fluently from an autocue and with the presidential seal in front of him, could have been coming from the White House itself. "We take off our Republican hats and put on our American hats," he went on. What a statesman!

Fourth, and in what may prove to be the most valuable of all the unlikely benefits Gustav and Hanna bring to the Republicans, the storms took much of the immediate public pressure off McCain's vice-presidential running-mate. I understand that the 44-year-old governor of Alaska, Sarah Palin - whose name McCain announced to a stunned world the day after Obama's fireworks - spent the hours closeted, out of the limelight, with party apparatchiks in St Paul, frantically trying to get up to speed on national and foreign policy issues for the hustings and, above all, for the much-awaited evening when she comes face-to-face with Senator Joe Biden at the vice-presidential debate in St Louis, Missouri, on 2 October.

At a stroke, McCain has seized much of the “change” territory

for himself

Inevitably, the dirt about Governor Palin was already flying. First came the national airing of "Troopergate," a saga that has already received wide publicity in Alaska: Palin has been accused of sacking the state's public safety commissioner because he refused to dismiss a policeman named Mike Wooten - Palin's former brother-in-law, who had divorced her sister and Tasered her 12-year-old nephew. Wooten has been reprimanded a dozen or so times since 2001, but because Palin herself has acquired a reputation for being incorruptible in a state that is notoriously corrupt, the story took off.

A calculated risk

Then, last Monday, came the "bombshell" that Palin's 17-year-old, unmarried daughter Bristol was five months pregnant - and was going to marry her high-school boyfriend, the baby's father. But in this peculiarly nasty campaign, the furore did not stop there. Blogs such as http://www.barackoblogger.com, as well as some in the mainstream media, starting putting out untrue allegations that Palin's own five-month-old son, Trig - who has Down's syndrome - is, in fact, the child of Bristol.

I wrote recently that Obama is taking a "colossal" risk in having Senator Joe Biden as his running mate, but it is nothing compared to that of McCain's risk when it comes to Palin. The two had never even met until February, when they had a 15-minute chat at a meeting of the National Governors Association in Washington.

But, despite the legions of Democratic and Republican operatives heading for Anchorage as I write, the McCain campaign insists that Palin's background had been carefully vetted, and that they already knew about Trooper- and Babygate; they say privately that they wanted both supposed scandals to come out early, so that manufactured furores in the final two months before polling day could be avoided.

The truth, though, is that McCain needed to do something dramatic to light fire to his campaign. Although he was holding his own against Obama to a degree many found surprising for a Republican in George W Bush's America of 2008, his campaign was not gaining traction. The problem facing him was that nearly all the obvious possible running mates were white men on the wrong side of middle age, such as former governors Mitt Romney (the choice until the last moment) or Tom Ridge - or even Senator Joe Lieberman, Al Gore's Democratic running mate in 2000 who has been drifting rightwards ever since and is now an Independent. The one remaining alternative was 47-year-old Tim Pawlenty, governor of Minnesota, but he is not especially telegenic.

So a woman it had to be. McCain seriously considered Meg Whitman, the 58-year-old founder and former chief executive of eBay, and Carly Fiorina, 53, the former boss of Hewlett-Packard, but neither had the necessary political instincts. He also needed somebody as young as possible to offset his own biggest liability - his age, now 72- and finally came up with Palin, 44, whose popularity ratings in Alaska have just soared to an unprecedented 80 per cent. By choosing her, the McCain ticket magically morphed into one that was, on average, only two years older than Obama.

McCain's announcement, which came the day after Obama's acceptance speech and stole much of his thunder, changed the entire dynamics of the race. The Obama team had prepared McCain-Romney, McCain-Lieberman, and McCain-Pawlenty attack ads, ready to be broadcasted across the nation the moment the Republican nominee made his announcement. But even they, the fastest-moving and most efficient campaign organisation since Bill Clinton's took President George Bush Sr by surprise in 1992, were not at all prepared for Governor Palin.

In one single strike, therefore, McCain had altered the thrust and direction meticulously planned by both sides. The Obama campaign had settled on a strategy of hammering away until election day on 4 November with the insistence that a McCain presidency would merely be a continuation of George W Bush's, constantly using the slogan "McCain the Same" in their two-month blitz of ads.

Suddenly, though, that argument weakened when Obama found himself facing an opponent whose running mate - rather than the stodgy old Romney or Ridge figure he had expected - was a self-described "hockey mom" and mother-of-five from Alaska, known to her basketball teammates in school as "Sarah Barracuda". The argument that the Obama-Biden ticket alone represented "change" also suddenly weakened; arguably, the McCain-Palin ticket now represented an even more seismic change.

For his part, McCain largely sacrificed his "experience" and "not ready to lead" arguments against the Democrats by choosing Palin. She, after all, did not even have a passport until she recently applied for one to visit Alaskan National Guard troops in Germany and Kuwait, so McCain could hardly continue to campaign against Obama by citing his foreign policy inexperience.

At a stroke, though, McCain had seized much of the "change" territory for himself: instead of two men in jackets and ties taking over the White House in 20 January as usual, he could argue that he is offering the prospect of a man and a mother-of-five in a skirt doing so instead. He had also positioned himself to steal a chunk of the non-ideological female supporters of Hillary Clinton, who are still chafing bitterly at the way Obama treated the Clintons; the database of Hillary donors would be like Alaskan gold-dust should it somehow mysteriously find its way into the McCain camp.

McCain's decision has also made life much more difficult for Biden, Obama's designated attack dog: at 65, he is from a generation still not comfortable with the notion of gender equality, and the possibility that he could bully and/or patronise Palin in the vice-presidential debate is a very real one. That alone would badly damage Obama, especially with female voters.

All of which is to say that we now have a new 2008 election on our hands, its dynamics and directions dramatically shifted. The supreme irony in the debate about Palin's lack of "experience" is that, compared with Hillary Clinton, McCain or Obama, she is the only one to have had actual executive experience of running anything: two years as governor of the nation's sixth most affluent state which is twice the size of Texas. This is the reason Americans have traditionally looked to governors, rather than senators or congressmen, to be their presidents; either McCain or Obama will be only the third president in history to have gone from the Senate to the White House (the others being Warren Harding in 1921 and JFK in 1961).

It is too early to say what Palin's arrival has done to the persistently close poll figures; Obama's extravaganza appeared to have given him little or no bounce until 1 September, when CBS found him five points up from before the Democratic convention. That gave him an overall lead of eight points, the largest so far.

Daily tracking polls, though, still showed Obama with statistically insignificant leads, ranging from one to six points. These polls mean little, in any case, until each party has had its convention enthroning its candidate and his running mate, and the real, post-Labor Day battle has commenced. Which means that next week we will have an altogether better idea of just how much the unexpected advent on the scene of Sarah Barracuda is affecting this most bizarre of US presidential elections.