In the final, post-debates stretch of a presidential campaign, regardless of who is leading, both sides are running on fumes. Nerves are frayed and tempers are short. Aides, strategists and staffers have been working around the clock. Tensions are triggered by the claustrophobia of spending waking and sleeping hours cooped up with campaign colleagues in a revolving door of airports, diners and cheap hotel rooms.

Even in the most highly disciplined campaign, the last few weeks are always the longest. This fatigue is mirrored by voters, who have been shocked into a sort of numbness by the daily rollercoaster ride that is the American economy and the candidates' daily pounding of each other. What started out as a thrilling and unpredictable campaign has become a relentless barrage of negative advertising, 'robo-slime' telephone calls warning of ties to terrorists and last ditch door-to-door sales pitches by feverish volunteers.

Even the candidates seem to be showing signs of wear and tear. Barack Obama's hair is noticeably tinged with grey. At indoor events, the lighting emphasises the dark circles under his eyes. His rival, John McCain, still brings a frenetic energy to the stump but he moves stiffly, almost painfully, at times.

The wealth of information and disinformation that has been put out by both camps, the myriad soundbites, slogans and images, the countless television appearances and impersonations on everything from Meet the Press to Saturday Night Live have been distilled into two very different personas. One plays poker. The other plays chess. In different times, McCain's roll the dice campaign might be invigorating, but for an America that doesn't feel especially lucky, it's enervating.

Two sides of a coin

Both campaigns' core messages are different sides of the same coin. McCain tells voters they can't trust Obama because they don't know him. Obama argues voters can't trust McCain because they do. Or rather, they know him well enough to know they don't know what he'll do next, never mind in a crisis. But it seems voters are shunning the devil they know for the devil they don't.

The three presidential debates, which drew 150 million viewers, completed the candidates' political metamorphoses: McCain has transformed himself from a national hero into an angry old man while Obama has passed the threshold from celebrity parvenu to plausible commander-in-chief. An American public, concerned that there was much they didn't know about Obama, found much to like, not least an unflappable equanimity.

The consensus, reflected in a slew of polls, that Obama emerged victorious from all three debates has left the McCain camp in something of a quandary as to where to go next.

Many Republicans believe that, barring a major misstep by Obama – and the political novice has made very few missteps during his campaign – or a major international incident, it will be very difficult for McCain to halt Obama's momentum between now and 4 November. It's a view shared by veteran Democrat Chris Lehane, who was Al Gore's chief strategist in 2004.

"He could run the greatest campaign in the history of campaigns and still lose by a landslide," Lehane said of McCain. "Given the current political environment, the Democrats could nominate a refrigerator and still win."

But Democrats, who have a proven track record of losing supposedly unlosable elections at the last minute, are nervous. Again and again last week Obama warned against complacency. Speaking at a fundraising breakfast at New York's Metropolitan club he reminded supporters of his surprise defeat in the New Hampshire primary earlier this year. "We cannot afford to be cocky," he said. "This is not the end of the hard work. It's the beginning."

Meanwhile, McCain's chief strategist, Steve Schmidt, seemed to concede something tantamount to defeat when he commented after the final debate, "The fact that we're in the race at all, within striking distance with a five per cent right track, is a miracle. Because the environment is so bad and the headwind is so strong."

This weekend, McCain's camp seized on what Schmidt believes may be a life ring inadvertently thrown to them by Obama. During an encounter with the now famous 'Joe the Plumber', who told Obama his tax plan would prevent him from being able to buy a plumbing business, Obama concluded an explanation of his tax policy by saying he wanted to "spread the wealth".

'Joe the Plumber'

It has since transpired that Joe the Plumber, whom McCain referred to 15 times during the debate as the personification of an ordinary decent American, doesn't possess a plumber's licence, owes back taxes and has as much chance of buying his own business as the rest of us have of buying Microsoft. But Obama's "spread the wealth" remark has been semaphored around the states still in play, via television ads, phonecalls and mailings.

"We're going to focus acutely on that," Schmidt said. "'Spread the wealth' was a big mistake."

Within the McCain camp, which has been riven by bitter infighting over the negative direction of McCain's campaign and his fumbling of the economic crisis, a view is emerging that suggests Steve Schmidt's appointment last July as McCain's chief strategist was an even bigger mistake.

"Hmmm. Let's see," said one McCain aide when asked by the Sunday Tribune what changes Schmidt had brought to the campaign. "Paris Hilton. Sarah Palin. Bill Ayers." The response, delivered with more than a hint of sarcasm, sums up neatly the divide and the dilemma that has convulsed the McCain camp for months. Some believe Schmidt has hobbled McCain. Others say that, without Schmidt, McCain wouldn't even be in the race.

McCain's Faustian pact

For months now McCain hasn't looked like a man in charge of his own campaign, never mind his own crowds. His inner circle, led by his chief of staff and long-time confidant Mark Salter, blame the emergence of a candidate who often seems angry and bewildered by his own strategy on a Faustian pact he entered into with Schmidt, a Karl Rove protégé and former spokesman for Dick Cheney who ran the war room for the Bush 2004 campaign.

Schmidt was recruited in July with the mandate of beefing up McCain's strategy. The Republican candidate had not made the transition from primary contender to national presidential candidate smoothly; his campaign was chaotic and lacked a coherent message. Schmidt's strategy was straight from the Rove playbook. It depended on two things. The first was the art of political jujitsu: turn your opponent's strength into his weakness. The second: use America's cultural divide to conquer.

Schmidt's first master stroke for McCain was an ad comparing Barack Obama to Paris Hilton. It was derided as silly and superficial but it certainly adjusted the media lens. To Schmidt step two was obvious: Reignite the culture wars and ratchet up the fear factor. And who better than Sarah Palin, the telegenic, right-wing conservative, to do both? Sources in the McCain camp say Salter was emphatically opposed to Palin's selection as McCain's running mate but Schmidt sold it to McCain on the basis that 'this is so out there it just might work'.

McCain, who is by no means risk-averse, bought into the Palin Hail Mary, and for a while the gamble seemed to have paid off beyond even Schmidt's wildest dreams. It levelled Obama's post-convention bounce and catapulted McCain ahead of Obama in the polls. But as the economy tanked, so did the public infatuation with Palin. A series of disastrous interviews prompted even long-time Republicans to suggest that McCain's selection of her was irresponsible, even reckless.

As McCain's numbers started to spiral, Schmidt used Palin to ratchet up attacks on Obama, designed to stoke fear in the minds of voters. Allegations that Obama was "palling around with terrorists", suggestions he was "unAmerican", fired up the crowds at McCain-Palin rallies.

The increasingly ugly mood at his events alarmed moderate Republicans, who urged McCain to change the tone of his campaign and rein in Palin.

Salter persuaded him he was squandering his reputation for no gain. It's one thing to sell your soul and win an election. It's quite another to sell your soul and lose it. McCain, engaged by the besmirching of his reputation and plummeting approval ratings, agreed, and with his boss back in his corner Salter told senior aides he would rather suffer an honourable defeat than conduct a campaign that was out of character and likely to make him lose the election.

Strained relations with Palin

Meanwhile, relations between Palin and McCain have become increasingly strained. A campaign source said her remark to conservative talk show host Rush Limbaugh that she had "nothing to lose" by continuing her attacks on Obama led to a heated showdown between the running mates.

With McCain veering away from personal attacks, and time and funds running out, his options are limited. On Friday evening, Schmidt said they were focusing on "a narrow victory scenario" where they would focus on the key battleground states of Virginia, North Carolina and Florida, as well as Ohio, Colorado, Missouri and Nevada. All seven are must-win states for McCain and this weekend Obama was ahead or tied in each one. He was also making inroads in West Virginia, a state that has been firmly in the Republican column since 1964.

Barring a cataclysmic domestic or international event, McCain's path to a narrow electoral college victory hinges on his winning all seven states. It's a tall order but, given the formidable odds against Obama and McCain emerging as their parties' candidates, never mind the implausibility of Palin's presence on the Republican ticket, the 2008 race has shown that, in US politics, the most unthinkable scenario is often the one that happens.