When half of mankind seems lifted by hope, nothing looks meaner than to disparage the dream. But what is this Obama mania? The world did not change for ever on Tuesday. No messiah has come among us. Miracles have not become possible. There is no new dawn. Calm down dear, it's only a US presidential election.

Here's my entry for Daniel Finkelstein's Comment Central competition for an eight-word expression of hope for the President-elect of the United States. Eight words precisely. “I hope he will let us down gently.”

But oh, what a long way down: down from the crest of expectation on which Barack Obama now surfs, on to the rough shingle of daily politics. Would that the wave might subside smoothly into the gentle swell of history. Would that it were not destined to break, dashing dreams and spawning new cynicism.

But I fear it will. Writing from Australia, and reading the local and the British press reaction to this election, I am appalled by the unanimity.

'Change has come' - Obama wins in landslide

Sweeping victory for America's first black president is greeted by tumultuous scenes Watch our video

• Analysis: Barack Obama's victory is head-spinning stuff

• Full video and text: Barack Obama's victory speech

• Early US Election exit polls give hope to Barack Obama

Michelle Obama: a new type of First Lady

For Carla Bruni the game is finally up. In Michelle Obama she has truly met her match - a First Lady like none before

BACKGROUND

• Bush - 'We should all be proud of Obama'

• The challenge that greets Obama

• Full video and text: Obama's victory speech

• Voters honour Martin Luther King's dream

Multimedia

• Team Obama - who are they?

• Bonjour 'Barack'

Yesterday I tried googling the name Obama with the phrase “President of the world”. There were 552,000 entries. In hopes of astringency I tried the leader column of The Daily Telegraph. “He is not so much an American citizen as a citizen of the world,” I read. “America, welcome back into the world,” gushed The Guardian, speaking for the world.

I turned to the Australian media. A spokesman for the Aboriginal community explains that the President-elect will have a special place in his sympathies for Aborigines. While Gordon Brown hopes the President-elect will have a special place in his heart for a British Labour Government, the Australian Prime Minister, Kevin Rudd (says the sobersided Australian Financial Review), believes special attention can be given to the US-Australian alliance “now Barack Obama has won”. Malcolm Turnbull, the Australian Leader of the Opposition, says Mr Obama's victory represented “a defining moment in history”.

“The election of Obama is when the old world ended and the new world began,” I read in the Australian Daily Telegraph. Kenyans look to Mr Obama for the President-elect's special attention. Gays note that he specially mentioned us in his victory speech.

So many alliances strengthened! So many special places in his heart! But why beat about the bush? Oprah Winfrey doesn't. “This is the most meaningful thing that has ever happened,” she gasps.

Useless, I know, to argue with infatuation, but I'll ask anyway: will we never learn?

Why, when we've been disappointed so often, do we fall for it every time with leaders? Here we have a handsome, dashing and intelligent man, a man with generous instincts and a silver tongue; but a man with no distinctive plan for government that he has seen fit to share with us; a daring opportunist; somebody we may one day judge as a sort of Tony Blair with brains. And here we go again, all over again, hook, line and sinker.

How quickly we forget that politics is not another world, where the laws of nature can be suspended and magic is possible. Circumstances constrain and events can be very compelling, and “Yes we can” is no gravity-defying abracadabra. It's when a leader has to move from “Yes we can” to “No you can't” that he is tested.

And that's to come. For now, before decisions have to be taken, there is no power greater than the power of tabula rasa. This is the potency of the blank slate; the new kid whom three British party leaders squabbled at Prime Minister's Questions this week to claim as their kind of guy; the individual into whose open countenance and easy smile we read all our hopes, and who reflects back to us what are really our own dreams. He, we sense, understands. He cares. He is like us, understands us, surely agrees with us, even though he has not yet said so. He would be our friend if ever we were to meet him. In some strange way he knows us already, though we have never been introduced.

He is the pop star whose poster adorns the adolescent's bedroom wall; the Blessed Mary who understands her supplicant's every woe; the gentle Jesus, a personal friend who will not forget us; the David Beckham who is surely deeper/cleverer/gayer/more cultured (depending on your bent) than he seems; the Queen Mother who, if she ever had come to tea, would have got on with us like a house on fire.

It is desperately important that we never meet these people, for reality would be cruel. We thought they knew our joys and woes, heard our prayers, and when it dawns on us that the demigod at whose feet we laid them hasn't listened, can't help, or doesn't care, our sense of rebuff will be personal. In our minds we were friends. Believe me, the disillusion when Elton John looks bored to meet you and turns away can be bitter.

There is no limit to the adoration of the potential fan club for an individual who - in myth or reality - can present a welcoming, receptive but essentially blank face with warmth, with charm, and perhaps a little guile too. Be that face and tremendous power will be transmitted through you, for you will be reflecting - back upon those who sent them - a million prayers.

But answering them is quite another thing. So let's get this straight. Barack Obama has not been elected President of the World; the world is not his constituency; and his responsibilities to the world are secondary. He is President-elect of an important but declining power, and his responsibilities, especially in hard times, are to its citizens. He will anyway be immensely constrained through the mechanisms of the American Constitution, by domestic opinion; his popularity may be at the mercy of the economy; and the American people, though plainly beguiled by his freshness and charm and their own despair at the alternative, have not this week been transfigured into liberal internationalists. In the day they were electing Mr Obama, many states were rejecting gay marriage by clear margins.

And this whole thing could go very sour. A politician who has subtly insinuated himself into the imaginations of millions as a secret friend and the personal champion of all their hopes for the world may find their disappointment the more bitter in the end.

Each of us in our private chapel half believes that Barack Obama knows our hopes and has heard our prayers. In his own person he has this week become - in a way of which Labour's 1997 victory was a faint and flimsy foretaste - the agglomeration of people's hopes and prayers. He is their prayers. He is their hopes.

But are their prayers consistent, their hopes achievable? In politics it is not enough to be the earnest expression of a wish, however eloquent. You also need a plan for granting it.

Does he? If not, and this was just another election, then I wonder how he'll break our hearts.

Times Recommends

• Care in old age: we won’t pay, the State can’t
• Viewers’ choice: our talentless Everyman
• Memo to the poor: go forth and don’t multiply