“Comments? Anyone?”
Why would they want to attack the US with an EMP?
I doubt that any other country will bother to keep sending them food.
On your questions as to the motive, what makes you think that logic would enter into the equation?
Very highly probable China has strategically prepositioned EMP devices. No fuss no muss.
A moment after, ha, they will wait a year until American society has totally chaotically dissolved. Then they willl recolonize the new world.