In a well-worn phrase, Marx wrote that history repeated itself, first as tragedy and then as farce. What we are witnessing at present, in the form of the Government and the Prime Minister, is both at once: a political farce, and a human tragedy. The farcical collapse of our government can be contemplated with detached amusement, but the personal disintegration of Gordon Brown is awful to behold.

Early yesterday morning Labour won Glasgow North East, in what one headline bizarrely called a "landslide", the word normally used for when a governing party is routed. What had actually happened? The Government had held one of the safest seats in the country, a rotten borough in a Third World region which Labour has dominated for generations by patronage, in a very low turnout after a campaign fought entirely on parochial issues. It's a mark of Brown's plight that this should be regarded as a triumph.

And anyone who thought that he was back in command had only to wait for the Prime Minister to be interviewed on Today. He was very weakly interviewed, as it happens, by Evan Davis, a first-class radio journalist in his proper métier of economics but badly miscast in this role. As Brown was allowed to prattle on, he must have given thanks that he wasn't being cross-examined by the ruthlessly forensic John Humphrys.

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Even so, what the Prime Minister said was embarrassing. The mood of the country is swinging strongly against the war in Afghanistan, and this is going to be a grave problem for the Tories when they take office. David Cameron should take heed, and try to avoid an argument – that the Grenadier Guards in Helmand are making British streets safer – so obviously fatuous as to discredit anyone who makes it.

But then it's of a piece with the whole story of this Government, under Tony Blair and then Brown, which increasingly appears a chronicle of missed opportunity and downright failure. A needless and illegal war in Iraq – in which Brown was closely complicit – is only part of it. Every day we are reminded that the economic miracle of which Brown once boasted so repetitiously was fraudulent.

As a result, Brown is now more enfeebled than any prime minister within living memory, or maybe in our history. Although John Major was said to be "in office but not in power", he seems in hindsight a towering figure compared with Brown, whose government is disintegrating around him, and who to a unique degree totally lacks authority.

For some time past the parliamentary Labour Party has been contemptuous and disobedient. The latest demonstration of this comes over the expenses scandal. Brown tells his MPs to accept their punishment, and they – contemptibly, but tellingly – tell him to get lost. His own ministers openly dissociate themselves from his policies, such as they are, in complete defiance of the fundamental principle of collective cabinet responsibility.

Not only do former heads of the army publicly criticise the Prime Minister, so does General Sir Richard Dannatt while still chief of defence staff. This has been quite rightly condemned as outraging an even more important principle, that of military subservience to the constitutional civilian government, but the political significance was missed: like MPs and ministers, generals feel no need to show any respect at all for Brown's authority.

It was always easy to foresee why Gordon Brown would be such a failure as prime minister; if anything, what's curious is that so many people were unable to do so, and persuaded themselves for so long that he would provide a quite different and more inspiring kind of leadership after the discredited Blair.

The key is something Felix Frankfurter, the Supreme Court justice, said of the newly elected President Franklin Roosevelt after meeting him in 1933. He had, said Frankfurter, "a second-class intellect but first-class temperament".

Many years after FDR, the late Roy Jenkins borrowed those words and applied them to Tony Blair, whom he much admired at first (though not for good). And Jenkins added that this wasn't an insult, since that was a better combination for political leadership than the other way round. Since then his point has been given far greater emphasis. Brown is precisely that, but the other way round.

Even if his reputation as an intellectual in politics was at one time greatly exaggerated by his sycophantic claque, there's no doubt that in an academic, exam-passing way he is a cleverer man than Blair. But Brown utterly lacks the temperament for high office. If he isn't taking uppers, downers or any other psychotropic drugs, as he assured Andrew Marr, perhaps he ought to be. He is not quite a nervous wreck as yet, but he too often looks and sounds like a man on the verge of cracking up.

His public decline – and his ritual humiliation – has been a horrible sight: humiliating for us who witness it as well as for him. Brown won some sympathy last week thanks to the disgusting way he was stitched up by The Sun. (Connoisseurs of that newspaper will have enjoyed its saying that, when Brown rang Jacqui Janes to apologise for the mistake in his letter of condolence for her son's death, she did what any normal mum would do, and began recording the conversation.) But even then, it was excruciating to hear him call himself "shy", and gauchely allude to his daughter's death.

After that, back to business as usual. Shortly after his completely implausible defence of the war, we were told that "Gordon Brown will try to persuade other European leaders to commit more troops to Afghanistan". Don't hold your breath – but do wonder what on earth the purpose of this Government is, and how much longer we can bear to watch this self-destruction of a creature of flesh and blood.

A book has been published in America called The Bush Tragedy, and I myself wrote an essay for The Atlantic Monthly five years ago called The Tragedy of Tony Blair. In truth, neither of those begins to match the tragedy of Gordon Brown.

wheaty@compuserve.com