Its actually quite simple, in terms of technology, navy, airforce, special forces, the US is unparalleled (With OBAMA in the office it might change though). In an all out war, crippling china could be done withing weeks from the defense line near JAPAN, bombing the coastline would destroy all their economic production sites and would devastate all their urban areas and military instalments. A few surgical stirkes could destroy the vast majority of their ICBM bases (The US could do that with their stealth capacity). China would react by sending as many troops into the battle, hoping that they would break through, but with their navy carrying them and their airforce supporting them, it would be an easy battle for the US. By this time people in China would start a popular revolution as even the little that they had would be taken from them due to war. Not to mention that the US economy could quickly adapt to war (Weve done it a few times before). History has showed us that the one thing Americans need to be the best is a good, inspirational leader (Reagan or Lincoln-like), unfortunately we dont have one yet.