In the film, The American President, the president's speechwriter Lewis Rothschild (played by Michael J Fox) appeals to the commander-in-chief to take a firm, clear stand against the Right. "People want leadership, Mr President, and in the absence of genuine leadership, they'll listen to anyone who steps up to the microphone." he says. "They want leadership. They're so thirsty for it they'll crawl through the desert toward a mirage, and when they discover there's no water, they'll drink the sand."

The president (played by Michael Douglas) retorts that the American electorate's problem is not a lack of leadership but an undiscerning palate.

"We've had presidents who were beloved, who couldn't find a coherent sentence with two hands and a flashlight," he says. "People don't drink the sand because they're thirsty. They drink the sand because they don't know the difference."

As the faithful wait in line in small towns across the country (some for more than a day) to see Sarah Palin on her book tour, the question of whether the US is deprived of a competent political class or gets the leadership it both deserves and truly desires seems as pertinent as ever.

On the one hand there is roughly between a quarter and a third of America that will clearly believe anything. That is the figure that strongly approved of George Bush's handling of the economy last year after the collapse of Lehman Brothers and the bailout. That same figure, in the immediate aftermath of hurricane Katrina, believed that Bush's response to the disaster was "about right", and still supports the war in Iraq.

That also happens to be approximately the same proportion of Americans who back Palin for president. Most data suggest the overlap is considerable. Palin's rise to prominence, from little-known governor to one of the most popular and arguably most charismatic Republicans in the country in just a year, has been startling. She had a thin record when she was picked to run as vice-president. Today, having quit the Alaska governorship mid-term and published a bestseller, only her wallet is thicker.

Her resignation speech was so rambling that you would have struggled to find a coherent sentence with an industrial-strength searchlight. "Let me go back to a comfortable analogy for me – sports," she announced. "I use it because you're naive if you don't see the national full-court press picking away right now: A good point guard drives through a full court press, protecting the ball, keeping her eye on the basket ... and she knows exactly when to pass the ball so that the team can win." This was not the answer to a hostile interview from the "liberal media elite" but a prepared speech of her own making.

It would be easy to discount her as just a media phenomenon who would go away if we stopped talking about her. That would be a mistake. It would be even easier to poke fun at her as just a small town hick who has blundered into the limelight with a nod, wink and a "you betcha". That too would be a mistake.

For the very things that liberal commentators ridicule her for – being inarticulate, unworldly, simplistic and hokey – are the very things that make her attractive to her base. Indeed, every time she is taunted she becomes more popular because it reaffirms the (not entirely mistaken) view that the deeply held values of a sizable section of the population are being disparaged.

The same dynamic was true for George Bush, but with one crucial exception. Bush is the scion of a wealthy family who turned his back on the cultural trappings of his class while embracing the social confidence and political and financial entitlement that came with it. Palin had none of those advantages: she grew up far from power and privilege in every sense.

The difference in their comfort levels when put on the spot with simple questions was evident when each was asked about their newspaper reading habits. Bush was cocky: "The best way to get the news is from objective sources. And the most objective sources I have are people on my staff who tell me what's happening in the world." Palin froze: "I've read most of them … all of them, any of them that have been in front of me over all these years."

In her world, Ivy League is a slur; cities are not the "real America"; and those who know the price of arugula but cannot handle a rifle are not to be trusted. Palin is the antithesis of an aspirational figure. Her supporters love her not because they want to be like her, but because they already are like her. So for better and for worse, Palin is an entirely self-made – and, if her book is anything to go by, self-invented – personification of the kind of political animal Bush sought to both emulate and nurture. Bush was Palin-lite.

To that extent her performance over the past year has been more tragic than comic. Palin represents the thwarted aspirations and brooding resentment of a large section of white working class Americans. That is not to suggest that her supporters are necessarily racist, but polls show her support is racially exclusive.

Her base has plenty to be resentful about. Their wages are stagnant, their economic security has eroded, and their prospects for social and economic advancement have stalled. In 2004, white Americans were the only racial group for whom the poverty rate actually rose. The fact that it was lower than every other group is of little comfort. Demographically, they are set to become a minority by 2042. Geopolitically, the country for which they display so much patriotic fervour has lost one war, is losing another, and is regularly lectured by others about the urgency of putting its fiscal house in order. America is not what it used to be. The country they keep saying they want to "take back" no longer exists and is not returning.

So when Palin rails against Washington DC, bank bailouts and elitist media she catches their ear. The longer unemployment keeps rising, house prices keep falling and universal healthcare continues to be elusive, the more ears there will be. Motivated, organised and angry, Palin's wing of the Republican party does not have the numbers to make bad things happen; but, as it showed over the summer during the healthcare town hall meetings, its determination to derail good things should not be underestimated.

The trouble is that while many of their grievances are well founded, their affection is certainly misplaced. None of their problems can be remedied by the politics championed by Palin. Indeed, the greater the traction her politics gets, the worse things will be for her base. The America whose passing they mourn was lost precisely because of the freemarket, low-tax, warmongering agenda she advocates.

To crawl through the desert in search of water only to find sand is disappointing; to not know the difference between water and sand is delusional; but to go looking for sand in the belief that it will truly quench your thirst, not once but twice, well that is truly depressing.