At the invitation of Prime Minister Shinzo Abe, U.S. President Donald Trump will travel to Tokyo on Saturday as the first foreign leader to meet newly enthroned Emperor Naruhito. This unique honor caps off Abe's campaign to develop a close personal rapport with his famously mercurial counterpart — including nominating Trump for a Nobel Peace Prize and presenting a set of gold-plated golf clubs to the bling-happy leader of the free world.

Such largesse is not without its reasons. Japan relies on its alliance with the United States for its national security and, although China has become its largest overall trade partner, the U.S. is Japan's largest export market. This is a bilateral relationship that Japan cannot afford to lose.

Yet the Trump administration presents unique challenges for Tokyo. Not only did the administration impose steel and aluminum tariffs on Japan last year, but it forced Tokyo into bilateral trade talks to avoid even more damaging tariffs on autos and other goods.