Most experts say if there were signs of this happening, the U.S. government would go for a combination of persuading Americans to buy more U.S. debt, the same way they did in World War II, and finding friendly foreign governments to make additional purchases.

Banks could be called on to increase their holdings of treasuries, and as a last resort, the Federal Reserve could also be called on to fill the gap, though this could risk turning any dollar weakness into a slump…

Beijing could also justify pulling back sharply from U.S. Treasuries if the dollar were to plunge, perhaps because of Washington’s failure to curb its budget deficit and debt.

“I worry that we could be at a tipping point,” said Eswar Prasad, a Brookings Institution economist and former International Monetary Fund official with responsibility for China.

“If the Chinese say ‘We’re not buying any more Treasuries,’ this could act as a trigger around which nervous market sentiment coalesces,” he said. “People could start wondering how the U.S. is going to finance its deficit.”