As Onionman mentions, the tariff would be met by an equal or greater tariff, and the US is a net importer from China. So we would end up even worse off than we are now but with a lot more paperwork. Tariffs are a kneejerk response that never ends well, and we just finally got into an economy not groaning under the weight from tit-for-tat penalties. Basically as the Chinese economy develops into a knowledge and industry rather than a raw material and cheap-labor economy things will balance themselves. Interventionist approaches by either the US or China have never ended well.
They would hurt themselves just as much as they hurt us, probably more. There is a reason China buys so much of our debt, because it benefits them. The US dollar, and US debt is some of the most coveted in the world, if China did start to sell, there would be ready buyers and China would be the odd man out. It is the same as owning 25% of a great company. If you try to sell all of it at the same time, there will be plenty of buyers to keep the price from crashing, but then what, you now own 0% of something that is very valuable and the only thing you can do is buy a company that is not as great.
