Ok, even before the Global Financial Crisis the USA had a huge trade deficit with China (and Japan?). Now that the US economy is in the tank and heavily indebted, obviously you are trying on many fronts to dig yourself out. Obviously China has long held a trade advantage over the rest of the world by artificially keeping its currency low. Whatever the morals of that, I have to say that this has probably helped take China from a third world nation to the developed nation it is teetering right on the brink of becoming today.
The US government is obviously feeling desperate if it is taking such an anti-free market step as to legalise the option of imposing tariffs on Chinese and Japanese goods and services.
Between it's GDP and more importantly its population China has just reached parity with the USA economically. Japan has has economic problems since the 1980s, after being an economic powerhouse in the decades previous to that.
Japan and China loathe each other with all their might, so much bad blood between them historically. China is taking tentative steps out of a firm anti-capitalist, anti-American ideology. Japan and the USA have WW2 between them, but also the successful McCarthy program that rebuilt and enriched Japan.
China is hell bent on regaining the democratic nation island of Taiwan, and the USA has committed itself to defend Taiwan from China. If the US goes ahead with trade tariffs, and an economic war erupts between the three nations... is this something the world can really afford right now? Could it escalate further into violence? I think China feels its ability to provide for its people is still too fragile to accept outsiders interfering with its export successes and continued large economic growth. Far too much of its population are still rural or urban peasants.