And the mood this week at a conference for investment advisers, not just from Bahrain but from all over the Gulf, was that they should be looking at as diversified a portfolio as possible, and should be thinking about investment in Asia.

This is important because, of course, the US has been relying on savings from oil producers in the Middle East, along with Asian savings, to offset its current account deficit. One of the reasons the dollar has been so weak has been the sense that international commitment to the US and to dollar assets has weakened. The US current account deficit actually began to narrow in the early part of this year, yet the dollar has become weaker.

Meanwhile, rapid growth in the developing world has sustained demand for oil, boosting the balances of oil exporters.

Latest figures from the World Economic Outlook, produced by the International Monetary Fund, show that the US current account deficit is more than 1.5% of world GDP; yes, that is world GDP, not US GDP.

On the other side of the balance sheet, the surplus of oil producers is more than 1% of world GDP. Thanks to the high oil price that surplus is at a sweet spot. It has shot up suddenly and the IMF thinks it will come down, at least as a share of world GDP. The IMF predicts that the oil price will come slowly down, so it follows that if present prices are maintained it may be understating the size of oil exporters' surpluses.

The figures also show what these flows are doing to the stock of foreign assets. The net asset position of the US gets worse and worse, not just in absolute numbers but as a percentage of world GDP, while the surpluses of the oil producers and emerging Asian economies (mostly China) keep on growing.

Is it likely the rest of the world will let the US accumulate debts equivalent to 12% of world GDP? Would the US itself be prepared to be so indebted, particularly as much of the debt will be to China and the Middle East? Surely not. But you have to ask what might stop it.

I happen to think the US current account may correct more swiftly than the IMF expects. I also suspect the investment community in China and the Middle East may diversify its portfolio more swiftly, too. If the second happens faster than the first, the dollar becomes vulnerable. For the dollar to fall, foreign investors just need to build up dollar assets rather more slowly.

Pause for a moment. The US will remain attractive to international investors for the foreseeable future.

That is not going to change. What is interesting is the extent to which Middle Eastern investors are now interested in other asset classes.

These include property, infrastructure and resources. The drying up of liquidity for private investments, from the perspective of the Gulf, is an opportunity.

India appears a particular beneficiary, more indeed than the rest of Asia. The point was made to me by a Qatari banker that India had many attractions for Gulf investors.

We are also going to see much more Gulf money in Britain and Europe. You can see what has happened to the euro as a result of this rebalancing of investment between dollar and euro assets. That leads to the biggest issue of all: how open will the US remain to foreign investors?

One particular area of concern is the extent to which so-called sovereign investment funds . . . funds accumulated by countries rather than private investors . . . are allowed to invest freely. The US is concerned about such investment, particularly since some of the countries concerned are regarded as hostile to American interests.

There are legitimate reasons for concern. Foreign governments can not only mobilise funds on a huge scale, they can also have different objectives to private investors. But restrictions on sovereign funds can scare off private investors, too, particularly if they appear to be applied capriciously. I don't think people in the US have any idea of the damage done by the blocking last year of the bid for P&O by Dubai Ports, on the grounds that the former controlled ports on the US east coast. Learning that you were not welcome by people you assumed were your friends was a salutary experience for investors in the region.

The result will be that investment in the US will carry a handicap. The US has the advantage of the size of its market and the predictability of its legal system. Some of that will be offset by this sense that foreign investment may be unwelcome. So the US will have to offer higher returns to attract international savings. A lot of the dollar's decline this year may be the result of this handicap. That will force a faster adjustment on the US than would otherwise be the case.

This may be no bad thing. It is not reasonable that the world's richest country should rely on the savings of poorer countries to maintain its lifestyle. The decline in the dollar may force countries that have linked their currency to it to cut loose. But you don't want adjustment to be too sudden. It is in no one's interest that the dollar should fall uncontrolled . . . and that danger will remain until the US becomes less reliant on savers in the rest of the world, including the Middle East.