His name might not be on the ballot paper, but the congressional midterm elections on 2 November will be a nationwide referendum on Barack Obama's presidency. The opinion polls suggest that the president's party is heading for a heavy defeat, with the Democrats at risk of losing control of both the Senate and the House of Representatives to a resurgent and reactionary Republican Party, aided by the populist Tea Party movement.

How did it come to this? Perhaps, as the columnist Frank Rich has argued, such was the hype and rhetoric that greeted his historic victory in 2008 that "the real Obama was destined to depreciate like the shiny, new luxury car that starts to lose its book value the moment it's driven off the lot".

Still, the rate of depreciation has been startling. According to a Harris poll published on 25 October, Mr Obama is facing the lowest job approval rating - 37 per cent - of his presidential term. More than four out of ten voters who previously supported the president have said they no longer back him. And independent voters prefer Republican Congressional candidates over Democrats by a margin of two to one. It is not true to claim, as the president's critics on the left and right do, that he has achieved little in his 22 months in office: the fiscal stimulus, financial reform and universal health care are admirable, if not radical, legislative achievements. But the Democrats' failure to promote these reforms effectively has led to the loss of crucial opportunities to win public confidence. Confronted by a hostile media, the orator-in-chief has been unable to communicate his message. (A recent poll showed that only 8 per cent of Americans were aware the president had given 95 per cent of US taxpayers a tax cut.)

But, above all else, it is the economy on which Mr Obama has fallen short. The latest employment figures showed that 95,000 workers lost their jobs in September, with the unemployment rate stuck at 9.6 per cent - despite Vice-President Joe Biden foolishly promising that the country would experience a "net increase in jobs every month". The administration can claim, with some justification, that its fiscal stimulus has prevented even greater losses. But that is of little comfort to the growing number of jobless and homeless Americans.

Mr Obama has faced attack from both sides: the left argues that the stimulus did not go far enough, while the right maintains that the deficit was increased for no good reason. But whether or not it is fair to blame Mr Obama is irrelevant. He is being blamed by many - including his own supporters. Even Shepard Fairey, the guerrilla artist behind the iconic and once-ubiquitous "Hope" poster, has said he is losing hope.

At a town hall meeting on 20 September, Mr Obama was left in no doubt about the depth of the discontent among Democrats. Velma Hart, a black mother, admonished the president for whom she voted in 2008 for failing to deliver the change promised. "I'm a mother. I'm a wife. I'm an American veteran and I'm one of your middle-class Americans. And, quite frankly, I'm exhausted," she said. "Exhausted of defending you, defending your administration, defending the mantle of change that I voted for and deeply disappointed with where we are right now." She concluded: "Mr President, I need you to answer honestly, is this my new reality?"

There is still time for Mr Obama to ensure that it isn't. He can draw solace from the experience of Bill Clinton, who recovered from a midterm drubbing in 1994 to win again two years later. The current incumbent also has the advantage of facing a Republican Party that is contemplating choosing, as its next presidential candidate, Sarah Palin.