Last week the Chinese Foreign Ministry all but confirmed that it plans to sell its longtime ally Pakistan a new 1,000-megawatt nuclear reactor. The deal, reportedly signed in February, is a cause for concern in Washington. Though nominally a U.S. ally, Pakistan already has the world's fastest-growing nuclear-weapons arsenal and one of the world's worst nuclear-proliferation records. It is a country perpetually under threat from religious fanaticism, political instability and economic mismanagement. The sale also poses a serious threat to the legitimacy of the international nuclear regulatory regime. Since 1974, the Nuclear Suppliers Group (NSG), a 46-member body, has been...