How long will China finance America?
China's foreign exchange reserves have soared.
In the second quarter of the current year, they rose by $178bn to $2.132 trillion to exceed $2 trillion for the first time.
According to Bloomberg this is a record increase.
On this occasion, the primary cause is not the great surplus of China's exports over its imports.
It's the result of overseas investors identifying China as the strongest of the world's major economies and pouring money into property and into shares: the Shanghai Composite Index has jumped 74% this year.
To put it another way, if international investors want to take an equity risk in these recessionary conditions, they go to China - because its economic stimulus package seems to be working (the annual growth rate in China in the three months to the end of June is said by forecasters to have been not far off 8%; we'll have the official stats, for what they're worth, tomorrow).
Now, the really interesting question is how much of that increment has been reinvested by the Chinese authorities into US government debt, or holdings of Treasury bonds and bills.
China is the largest foreign lender to the US government. At the end of April, China's holding of Treasury securities was $763.5bn (Japan was the second biggest holder, with $686bn).
However, between March and April there was actually a slight fall in the dollar value of Chinese lending to the American government - though that fall was trivial compared with the $261.5bn increase over just a year in the amount of US government bonds held by China.
A recent speech by Zhou Xiaochuan, the governor of the Chinese central bank, conceded - in a slightly elliptical way - that China would have to lend more to the US, to see it through the current economic and financial crisis.
He said: "in the short run, the US may need more capital inflows to deal with the financial crisis".
So China will continue to fund the growing gap between America's public expenditure and its tax revenues, by recycling to the US the cash of overseas investors who prefer to invest in China's real assets.
Mr Zhou is clear that allowing America to live beyond its means is profoundly unhealthy for the global economy in the long term.
As he said: "over the long run, large capital inflows are not in its best interest of making adjustments to its economic growth model".
Or to put it another way, the US public, private and financial sectors all have to reduce their indebtedness: Americans have to save more.
But there is huge self-interest on the part of the Chinese in not forcing America to go cold turkey - in breaking its borrowing addiction - too quickly. China's exporters, squeezed savagely over the past year by the global recession, would hardly relish another lurch downward in US demand for their stuff.
The interdependence of China's great production machine and America's army of consumers remains the great fact of the global economy.
So although the Chinese authorities would love to hold their reserves somewhere other than in dollars (and Mr Zhou is a great proponent of enhancing "the status of the SDR" - the IMF's virtual currency - as an alternative to the dollar), it won't be quick or easy for China and America to reform their uncomfortable relationship of dealer and user.