The remark was quickly followed by a statement from Japanese Prime Minister Shinzo Abe denying that his government would even consider the matter, and by assurances from U.S. Secretary of State Condoleezza Rice that the United States is committed to providing for Japan's defense.

In floating this idea -- retractions aside -- Japan could be trying to send a message to China. The possibility of Japanese arms proliferation (and the larger specter of a Northeast Asian arms race) scares Beijing, and is one of the few possible hopes for leveraging China into taking a more proactive stance on North Korea.

China has more ability than anyone else to control North Korea, yet the six-party talks have been unsuccessful in persuading China to use that power. Even following Pyongyang's Oct. 9 nuclear test, China has refused to join strong sanctions proposed by Japan and the United States. As we have said, that is because China's national interest doesn't require it to take action against Pyongyang; but the prospect of a nuclear-armed Japan could change that calculus.

Japan and China have a long history of competing for regional primacy in East Asia. China, for its part, still bitterly remembers the Japanese invasion in World War II. More recent Sino-Japanese competition has taken the economic route; Japan has had no real military capacity outside of its self-defense force, and that suits China just fine. If the Japanese respond to North Korean nuclear proliferation by pursuing a bomb of their own, it would open the old wounds of history and set off alarm bells in Beijing.

Of course, a lot would have to happen before Japan would take that leap. For obvious reasons, the Japanese are very anti-nuclear; they don't even let nuclear powered -- let alone nuclear-armed -- U.S. Navy ships into their harbors. Developing nuclear weapons of their own would represent a reversal of 60 years of governmental and social thinking. However, Beijing has to consider that Aso's statement could in fact indicate the beginning of such a reversal; and if it wanted to, Japan could likely develop a nuclear weapon in less than a year.

A Northeast Asian arms race would not stop at nuclear proliferation, and would have serious economic implications. While Japan might be able to afford an increase in defense spending to manufacture the high-tech weapons necessary to sustain an arms race, China could not. Beijing is not prepared to handle a regional crisis on top of its domestic problems. It does well just to stay afloat despite massive unemployment, social unrest resulting from an increasing wealth gap and a banking sector saddled with extensive bad loans. Billions of dollars of government expenditures to compete in an arms race could easily be the straw to break the camel's back.

Tokyo could be betting that, to avoid being trapped in such an arms race, China will finally start trying to rein in North Korea. That's a risky bet, given that even raising the possibility of forming a committee to talk about developing a nuclear weapon makes Japan's neighbors and allies jittery -- which is why Abe and Rice were so quick to contradict Aso's statements. At the moment, the talk of Japanese nuclear weapons is only rhetoric, and quickly retracted rhetoric at that. If North Korea tests another bomb, however, Japan might feel it has no choice to take its nuclear rhetoric up another notch