With the U.S. nuclear umbrella shrinking and nuclear threats in Asia greater and more complex, analysts cannot dismiss a nuclear armed Japan as a purely academic exercise. 

While we should not expect a Japanese nuclear breakout in the near term, Washington’s traditional reassurances-- massive numbers of weapons deployed in theater and a robust regional presence-- have given way to a less convincing reliance on specific weapon systems amidst a diminishing conventional military advantage.  Enhanced bilateral dialogue has been used to strengthen the alliance, but Japan’s neighborhood is more dangerous than ever, and the many domestic constraints on Japanese nuclear breakout-- cultural, political, and institutional-- could become less restrictive than before.