Six months ago, the White House was weighing up an enviable problem: when do you get to start celebrating an economic recovery? The administration's chief economist at the time, Austan Goolsbee, had announced that the US had "turned a very serious corner". The Democratic strategist Paul Begala told me the "hard part" was to cheerlead the "nascent recovery" without appearing out of touch. I wrote a now-ludicrous story casting Barack Obama's dilem­ma as being when and how to declare victory.

That assumption was not limited to Democrats. The Republican presidential candidate Mitt Romney warned a private Republican gathering a year ago this month that Obama "will do everything he can to get the economy going back again, and most likely - at least in my view - the economy will be coming back". Romney told Republicans that they would have to make the vaguer case that Obama "has not understood the nature of America".

Obama took office with what looked like enviable timing. Americans had chosen the candidate of change in bad times and, when recovery inevitably took hold, he would get the credit. That was the formula for Ronald Reagan and Bill Clinton. In 1995, Clinton's aides had the same debate Obama's had this winter. They convinced Clinton to declare economic victory, and he helped turn favourable economic numbers into an optimistic national mood.

Numbers game

Economists and politicians will debate why the US recovery flagged this spring. Critics on the right say Obama should have cut regulations and taxes, not passed a new health-care plan. Keynesians to his left say - as they have said for two years - that his "stimulus" was simply too small. That question of blame will be central to next year's presidential campaign.

Reagan and Clinton were both years in to real booms when public perception caught up with economic reality. Obama's aides like to note that poll numbers for every president of modern times have dipped below 40 per cent - as Obama's did last month for the first time in Gallup's survey. But neither Reagan nor Clinton had ratings this bad this close to an election.

So, Obama's supporters and foes alike have begun to contemplate something that has no place in the triumphal arc on which he seemed set when elected: Obama could well lose next time. The president's odds of re-election on the political gambling site Intrade were exactly even last weekend. And the online traders aren't the only ones gambling.

The sense of weakness has begun to ripple outward. For instance, Israeli and Palestinian leaders alike are acting as if there won't be another Obama term, rebuffing the most powerful man in the world without evident regret.

Obama ran for office and won it as the candidate of history and change - and that candidate never loses. For that reason, it may have taken unusually long for his lengthening odds for 2012 to sink in. The White House still projects political confidence and leading Democrats continue to stand with Obama publicly, but privately they are beginning to worry.

Although he remains overwhelmingly popular inside his own party, it's the independents he's losing. An unexpectedly tight congressional election in liberal New York City is the latest bad sign: the voters, unhappy with Obama, are taking it out on his allies.

One recent weekend in New Hampshire, it was easy to see the path to an Obama defeat. He won the state by 10 percentage points in 2008. Now a series of statewide polls shows him trailing Romney - who has established his residence at a local vacation home. Romney may not survive the arrival of the staunchly conservative Rick Perry in the Republican primary, but Perry's entry into the race has, paradoxically, liberated the moderate former governor of Massachusetts to follow a more centrist path. At a sparsely attended Tea Party rally at a park in Concord, New Hampshire, Romney didn't let the words "Tea Party" pass his lips, and he hasn't offered the conservative grass roots any especially juicy red meat.

The next morning, Romney found his core supporters - more than 400 of them, an excellent turnout in the small-scale politics of the state - at a Manchester country club. They included people such as Susan Greeley. (Her husband is a distant cousin of the newspaper editor Horace Greeley, who said: "Go west, young man.") She voted for Obama in 2008, but will vote for Romney in 2012 if he is the Republican nominee. He is, she said, "balanced" and "level-headed". "I want somebody who's in the centre who can pull people together from both sides," said another Romney backer, Bill Gordon. "We'll tear this country apart if we swing all the way the other way."

Centre ground

These are the voices of swing voters swinging away from the president. And they aren't people who hate Obama - indeed, surveys show that more than 70 per cent of Americans like him, though only about half that number think he's doing a good job. While Perry projects the Tea Party's loathing - the president, he said recently, appears to be an "abject liar" - Romney has calibrated his pitch to the centre, where elections are decided. He speaks of Obama in tones of pity, as a man out of his depth. The president, Romney said in the Republicans' California debate on 7 September, is "a nice guy" who "doesn't have a clue how to get this country working again".

That's a powerful pitch to suburban working women like Greeley, who make up a vital bloc of swing votes and who may not warm as quickly to Perry's more sharply conservative views. It's a symptom of Obama's plight that his shot at a second term may turn on the decisions of Republican primary voters - yet another development over which he has almost no control.

Ben Smith writes for politico.com