Nuclear strategy has become a core concern in the US-Japan alliance. North Korea is the immediate trigger for Japanese anxiety, but similar uncertainties lie just beneath the surface when Japan contemplates China as well. US assurances are needed - both to Japan and to potential adversaries that need to be deterred.
Most important, however, is a 'back to basics approach' for the US and its alliance partners. Changing international circumstances and evolving domestic politics oblige Washington and its allies to focus on fundamentals of strategy to ensure that alliances have the foundation - the common world view - that will allow them to survive and thrive in a new strategic environment.
Japan has long nestled under the US nuclear umbrella. Throughout the cold war, America's extended deterrent provided the foundation of the US-Japan alliance: all potential enemies of Japan wrestled with the knowledge that an attack on Japan would trigger a US response and that a nuclear attack could include a retaliatory attack with nuclear weapons.
But North Korea's October 9 nuclear test has somehow raised doubts in Japan about the credibility of the US commitment to defend Japan or its ability to credibly deter Pyongyang. Fears of decoupling are behind comments about Tokyo considering its own nuclear capability or the acquisition of a 'strike capability' that would allow it to pre-emptively attack missiles on a launch pad.
Some in Japan see the US readiness to move forward in the six-party talks as signalling a loosening of the US-Japan alliance.
There is a growing view in Japan that the US will be satisfied with a nuclear weapons-equipped North Korea as long as its proliferation concerns are addressed.