Howard Jacobson: Could it be that the man who was foreverin waiting was never really there at all?

I'd be surpised if there isn't an hour of the night when Brown wonders if his vanity ever had any basis

Some jokes are so good so derisive, so wounding, so cruelly apposite that anyone with a grain of humanity would stop himself from laughing if he could. But that's the trouble with laughter: it won't be governed by what's fair, what's decent, or what's humane. Vincent Cable's reference, the other day, to the Prime Minister's "remarkable transformation in the past weeks from Stalin to Mr Bean" was just such a joke. Vincent Cable himself looked sorry to be making it. Which only compounded the cruelty.

You expect something killing from a wag like William Hague. But when a crestfallen man brings you down the acting leader of the Liberal Democrats, for pity's sake you're in deep trouble. Better an assassin who smiles as the knife goes in, than one who apologises.

But that's what Brown's reduced to now a dull and muddy-mettled rascal, who mopes like John-a-dreams and can say nothing. Who calls him coward, plucks off his beard and tweaks him by the nose? well Cameron does for one, indeed is allowed to get away with doing so to such a degree one wonders if it's all a ploy to show the Tory leader as a heartless brute. Though it's more likely that Vincent Cable's joke tells it how it is. Poor Mr Brown, whom we all thought would prove most royal, is not Prince Hamlet nor was meant to be. He's Mr Bean.

No accident that we hear Mr Has-Been in that. It was that kind of joke: it just went on working, echoing long after the laughter had died down. In fact I doubt there's anything new about invoking Mr Bean's ineptitude to ridicule a party leader. If I'm not mistaken they've all been Bean in their time. Dennis Healey's dead sheep was funnier for my money and probably finished off Geoffrey Howe more effectively than Mr Bean will finish off Mr Brown but Vincent Cable's particular stroke of comic genius was to yoke Mr Bean to Stalin. From Stalin to Mr Bean being a descent not just funny in itself, but wickedly so in relation to Mr Brown, from whom so much strong leadership in the name of stern socialistic principle was promised a heavyweight was how Blair described his successor but whose politics have so far matched his performance in barely rising above a whimper.

Thus in one swipe the joke not only charted a spectacular fall from eminence and expectation, but reminded us of the ideological inflexibility on which such eminence, were it any more to be enjoyed, was founded; thereby damning Brown for what he aspired to and for failing to reach it. You destroy a hero twice when you dash him from a great height, and then show that what he occupied was no great height at all.

We are, it seems, still deciding whether Brown is culpable or just unlucky as far as this latest scandal goes. That applies no less to Mr Bean. Is it down to bad luck or failure of character that he ends up with his head stuck up a Christmas turkey? Myself, though I'm not prepared to go the Freudian distance and say there's no such thing as accident, I hold the man responsible. It behoves one morally not to be so much of a klutz. Which just possibly explains why I've never found Mr Bean remotely funny while millions of others of all nationalities apparently do.

And Gordon Brown? Well it's beginning to look as though the Christmas turkey hasn't dropped out of the sky but is of his own contriving. Doubtless some will find the spectacle of his wearing it hilarious. But I suspect an altogether more tragic story is unfolding as we watch. Could it be that the man who was forever in waiting was never really there at all? In the unfairness, as he saw it, of his being brushed aside, in the arrogance of his conviction that he'd do the job far better than the man obstructing him, in his assumption of intellectual superiority, was there in fact no substance beyond pride and pique? Or did he wear away whatever substance he once had in frustrated enmity?

There's some secret at the heart of a profound rivalry that baffles all attempts to uncover it. "Demand me nothing," Iago says, after he has destroyed Othello. "What you know, you know. From this time forth I never will speak a word." So what do we know? That a rivalry of the Brown/Blair, Othello/Iago, Mozart/Salieri sort alchemizes hate and love, scorn and admiration, into a most potent poison. That the perceived loser by the relationship will stop at nothing to dethrone the victor. That the moment of revenge is not the sweet thing it was brewed to be. That both parties to the rivalry will be defeated. Thereafter they take what else they know into the grave.

Who, then, is going to tell us what Brown is thinking today? If he were honest would he acknowledge that such a rivalry as he enjoyed for so many wasted years was like love in being all consuming? Would he say that it destroyed his gifts, wore them away in ire and envy, or is he in possession of a crueller truth that the gifts he thought were his were all along someone else's? That he thought he saw himself denied in Tony Blair but actually only saw Tony Blair confirmed, and in the strange love he bore him mistook the other man's genius for his own?

In a cruel world one counts one's blessings every hour. So many places one would rather not live in, so many people one is grateful not to be. But I am especially thankful I am not Gordon Brown, for his must be a peculiar hell right now. The man is vain according to all accounts, but I'd be surprised if there isn't an hour of the night when he looks his vanity in the eye and wonders if it ever had any basis in talent or achievement.

Forget the Chancellorship that won't suffice him. The Prime Minister's is the job he always considered his by right. Not that grinning poppinjay's with an oily manner. And now look. What if Tony knew better how to do it all along? Knew at least how to ride a joke. For there's the cruellest part of it of all it doesn't matter how deep your intelligence or convictions, or how ingrained your sense of vocation and election, if you look sick when someone laughs at you, you aren't up to the job. Unless you're Stalin with gulags at your disposal. But what if you're not Stalin? What if you're Mr Bean?