May the Lord the former president so ostentatiously worships have mercy on my soul, and those in Iraq without water, electricity and medicine forgive me, but I just cannot suppress a twinge of sympathy for George W Bush.

The source of this pity pang isn't the usual one with those struggling bemusedly with the loss of power (Mrs Thatcher literally unable, for example, to dial a phone number). So far as the practicalities, Mr Bush has adapted well. Apparently he concludes his memoir Decision Points with the familiar anecdote of how, within days of leaving Washington, he was picking up his dog's mess with a plastic bag in a Texas park. Evidently he regards this as a cute vignette of the transience of power, as well as his own endearing lack of pomp. Yet what causes the stab of pity is the stupidity at which it hints.

How could anyone in possession of a three-figure IQ (still a moot point with Bush) fail to see what a golden gift that image is to satirists? There he is, in the cartoon in my head, scooping up a couple of Cumberland sausages while following him, shovelling up the Augean Stable-sized steaming pile he left behind in the Oval Office, is Barack Obama at the wheel of an industrial digger.

This blindness to visual imagery is quite a motif, judging by Times extracts and an interview with its editor. Apart from being attacked for indifference to black people by Kanye West, the rapper Obama dismissed as a jackass, all his greatest regrets are pictorial public relations disasters.

His sadness over Hurricane Katrina is not for the victims in New Orleans, as Mr West understood, but for the damage done to his reputation by that snap of him staring blankly and aloofly down on the catastrophe from the window of Air Force One. His paramount distress over Iraq is not over the loss of life, civilian and military, but how that banner proclaiming "Mission Accomplished" on the aircraft carrier came to make him look naive and vainglorious. He reveals his shallowness and vapidity with these reflections in the most crystalline of clarity, and hasn't a notion he is doing so.

It takes a certain minimal intelligence for the truly dim to have a notion of their own dimness, but this is denied him. Unlike Mr Tony Blair, who emerges from his well-calibrated if often chilling memoir as a man of colossal cleverness (though not intellect), W has the self-awareness of a bison. There seems even less to him than met the eye, and there was precious little of that. Astounding as it appears, we misoverestimated him.

And so the Wagner Question poses itself yet again. Every Saturday when the Brazilian sea monster murders his X-Factor song, 14 million people ask themselves how and why he is there. Reading these ghost-written titbits, you ask yourself the same. How in the name of all the saints did George W Bush, wastrel drunkard son of an East Coast patrician family, find his way to Pennsylvania Avenue by playing the genial good ol' boy from the South, and why in heaven's name did he want it anyway? And answers come there none.

The reduction of Bush's two terms to a satirical sequel to one of those US prep school movies in which the smirking, idiot boy breaks the honour code but is rescued by his Brahmin dad had come to seem shamefully hackneyed. But the one cliché worth trotting out here is that clichés are clichés because they are true. Somehow this half-witted frat boy journeyed, via some jovially preposterous sequence of events involving failed oil deals and baseball team franchises, from japes with Alpha Sigma Phi to possession of the nuclear codes.

Nothing, not even W himself, is ever quite that simple, and palpably there was an edge of madness in the family. In his teens, when his mother Barbara had a miscarriage, he relates, he drove her to the hospital. "I never expected to see the remains of the foetus," he recalls, "which she had saved in a jar to bring to the hospital. I remember thinking there was a human life, a little brother or sister." Enough in that alone, to drive any adolescent to drink, you'd have guessed, yet the tale is told as a homily to his mother's wisdom, and in some impenetrable way to justify his pro-life, anti-stem cell research hard line.

Almost every sentence in the Times extraction (and it does feel like having a tooth pulled) invokes a fatigued he-just-doesn't-get-it. Churchill is inevitably adduced, while W bangs on about his passion for reading history. Inevitably, he fails to make the connection.

"Study history, study history. In history lies all the secrets of statecraft," urged Winston, and while Bush did little as president other than read history books, the stagecraft entirely eluded him. Some of those tomes must have dealt with the British and Soviet experiences of invading Afghanistan, and not a word sunk in. I know how that feels from a tussle with A Brief History of Time. The difference is that I didn't extrapolate my failure to grasp a syllable into a bold attempt to rewrite the laws of quantum physics. He assumed he could rewrite the laws of geopolitics.

The process of historical revisionism has, like everything else, speeded alarmingly in the internet age. The emergence of Sarah Palin as an imaginable presidential candidate, allied to the unending travails of Obama, have induced in the amnesiac, the obtuse and the plain bananas a fondness for the memory of George W Bush.

It will not spread. If this great reader of history is concerned for his place in it – and that, needless to say, is why he hired a bright young groupie from Yale to write this memoir in something approximating English – he needn't fret. In those few lists ranking all the presidents compiled since he left office, W is invariably in the bottom five.