It's not as if Japan has any choice...
I'm sure that Japan would always prefer to work with a strong, democratic, and free market oriented America, over a Communist-led China.
But if Japan sees that America has become completely unhinged - it may very well decide to work instead with China.
China doesn't invade anyone, or kidnap anyone's presidents.
China doesn't come up with new tariff policies every time it wakes up in the morning.
China has only enough nukes to defend itself, but not enough to destroy the world 5 times over.
China doesn't tell its friends that they have to spend 5% of gross national product on their Chinese weapons - or else!
China doesn't try to make everyone buy ther gas or oil - instead they are the number one exporter of dirt cheap renewable technologies.
-//-
Mark Carney seems like a reasonable guy - and look at him.
He's your second largest trade partner after Mexico, and he's already seen and heard enough.
Not so hard to imagine that Japan may get tired one day.