Would Communist China pursue the “nuclear option” in a potential trade war with America? That’s the warning by Yale economist Stephen Roach. He’s not talking about A-bombs, but rather Beijing’s holdings of American debt. The People’s Republic of China, Mr. Roach says, could go on a “buyer’s strike” at Treasury debt auctions — or, worse, “start to unload its outsize position as America’s second-largest foreign creditor.”