There is no foreign and security policy challenge for Japan that tops divining U.S. policy toward China. Getting U.S. thinking right shapes ¡ª and in some cases, determines ¡ª how Tokyo deals with its neighbor.

That task is always difficult since Washington views Beijing from a different perspective and weighs a considerably larger basket of interests and equities than those Tokyo considers. It has become immeasurably harder in the Trump era, however, when the traditional decision-making process has been disassembled, the president¡¯s mindset is mercurial, his inputs ad hoc and he considers unpredictability to be an asset.

It¡¯s hard to appreciate the importance of U.S. policy toward China in shaping Japan¡¯s decision-making. As its sole ally, Japanese administrations are acutely sensitive to the U.S¡¯ readiness to act in their country¡¯s defense when threatened by Beijing. Those governments must navigate competing concerns: the fear that the U.S. will be too hostile toward China, creating and sucking Japan into regional instability, or too accommodating and ready to trade away Japan¡¯s interests in the name of a deal between the two great powers ¡ª a Group of Two.