China's leaders are worrying about the country's U.S. dollar assets. That's about all they can do. Chinese Premier Wen Jiabao on Friday used his annual news conference to fire a shot across Washington's bow, saying he's 'worried' about the safety of China's U.S. assets. His words sent a chill through the Treasury market, and urging the U.S. government to 'maintain its credibility' will ruffle feathers, too. China's central bank followed up later by raising concerns over the U.S.'s fiscal deficit. Rhetoric aside, it bears repeating that China will find it hard to make a meaningful shift out of Treasurys, the prime current channel for investment of its $1.95 trillion foreign-exchange reserves. Some say China could switch holdings into gold, but that market is highly volatile and not large enough to absorb more than a small proportion of China's reserves. It isn't clear if euro- or yen-denominated debt is any safer, more liquid or more profitable than U.S. debt -- key criteria for China's leadership. Even if China decided to sell some of its U.S. Treasury holdings, it would scarcely be able to dump that in large blocks. And a partial selloff would surely lead to a slump in the Treasury market, eroding the remaining value of China's portfolio. But whatever the rhetoric, Mr. Wen and his colleagues, like the rest of us, can do little but watch, wait and worry about the state of the U.S. economy.