Barack Obama surprised America this week when he let it be known that he was planning to nominate a television doctor as the US surgeon-general. In fairness, Sanjay Gupta is a qualified neurosurgeon, not a cast-member of ER. But his contribution to medicine has been somewhat less memorable in the past few years than his telegenic performances as CNN's medical expert. Morbidity plus good looks are sure ratings winners on TV news and Dr Gupta, with his handy graphics of the urinary tract has been quite effective whenever - “Breaking News”! - some celebrity is stricken with a horrible disease.

Now he will presumably bring these skills on to an official stage in the latest round of efforts to persuade Americans to stop eating too much and abstain from other self- destructive habits. Good luck to him.

Although it has its critics, it is a clever idea, if you think about it, to put a plausible and popular TV personality into a senior government post, and it has possibilities. Oprah Winfrey would make an excellent education secretary. Dr Phil could look after the nation's mental health. And, if you stretch the imagination a bit, Jack Bauer of 24 - minus the predilection to torture that regrettably seems to animate him - would be ideal for homeland security.

But what Mr Obama really needs right now is a television superhero to help him to rescue the US economy. His inauguration as president in 11 days' time will take place in what can be described, without hyperbole, as the worst economic conditions the US has faced in at least 70 years. Data due from the Labor Department this morning is likely to show that the US lost more jobs, net, in 2008 than in any year since the Second World War. Economic activity in 2009 is likely to decline at its fastest since the same historic landmark.

Most alarming, not only is there no obvious end in sight, the evidence suggests that things are getting worse. Despite the bailouts last year, the financial system, crippled by the housing market disaster and folly, remains clogged and more big financial institutions are likely to be in trouble in the next few months.

The American consumer, the hero of the global economy in every period of weakness in the past decade - from the Asian financial crisis to 9/11 - has gone on strike. Her carefree days of huge SUVs and $5 cups of coffee are over. Not only is she fearful of losing her job, if she hasn't already lost it, she can no longer expect to meet her long-term saving needs out of higher house and equity prices. So she is doing something she hasn't done in 20 years - saving. But what looks like frugal prudence for the individual family is deflationary disaster for the economy as a whole. As people cut spending, the downward spiral accelerates.

In the absence of an economic version of Dr Gupta or Jack Bauer, the President-elect has wisely opted for a huge public stimulus. Yesterday, in his biggest speech since election night in Chicago two months ago, Mr Obama laid out his case for what has been called, with dull predictability, his New Deal.

It's not exactly a replica of Franklin Roosevelt's measures to end the Great Depression but, in scale at least, it might prove to be of a similar order. The numbers are startling. This week the Government's budget economists said that the fiscal deficit for the coming year is likely to be $1.2 trillion. That is about 8 per cent of US national income. And it is before Mr Obama and the Democratic-controlled Congress have approved a penny of extra stimulus. The precise scale of the Obama plan is uncertain, but the combination of spending and tax cuts is likely to work out to be at least $500 billion a year for a couple of years. That would take the annual deficits comfortably above 10 per cent of US GDP. When FDR did it, such public largesse was still regarded by many as dangerous folly. Although there are a few worriers today, Keynesian demand-stimulus is more or less economic orthodoxy, so alarm about the scale of the fiscal effort is likely to be muted.

There are still risks, however. Set aside, for the moment, what might be called the reckoning - the need for the US Government, as soon as the crisis is past, to rein back the spending and avoid serious long-term damage to the economy.

An obvious risk is that the world might not be willing to pay for it. The US borrows the money it needs from the global financial markets, including a large chunk from foreign central banks. Should investors start to worry that a deficit of this scale threatens to rend the very fabric of US creditworthiness, they might demand a much higher price - through higher interest rates.

Fortunately, that risk still seems fairly low. In fact, as projections for the deficit grow larger by the day, interest rates on US Treasury bonds keep dropping to historic lows.

The biggest risk, oddly, is that this massive stimulus still might not be massive enough. While the US Government is borrowing like there's no tomorrow, the US private sector is cutting borrowing sharply. Not only consumers, but also businesses are shrinking their debt drastically at a pace that might match the increase in public debt.

As big as it is, therefore, the US cannot do it all on its own. A global crisis demands a global response. Massive stimulus is needed in Europe and very probably in Asia too.

The irony of this historic moment is this. Mr Obama takes office at a time of extraordinary hopes and expectations for his presidency from around the world. But if he is to come close to meeting those expectations he will need help, not hope, from the rest of the world.

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