Lets be real here, it will never come to blows with China.
The US Military has the capability to infiltrate or invade any country on earth regardless of size, population, or military technology. If for some situation war DID pop off, the 7th fleet could single-handedly along with our brothers in the JSDF destroy or disable all Chinese naval capability. The time of defensive borders and what not is gone. What the Nazis did 70 years ago, we are masters of. If that was lightning war, this is super sonic war. However unlike WWII, it would be much akin to Desert Storm or OIF, however with much more resistance. Infantry losses for both sides will be minimal for a long time. It would rockets, JDAMs and lots of CIWS systems going off at the same time.
China is due for a collapse, India will overtake them in both GDP and military might within 20 years. But realistically, at most, we could ruin their country through sanctions alone, although they can do the same through cyber warfare.
I am am as pro-war as you can go when Americans are attacked, but this is hypothetical that is just downright moronic because the chances of it happening are so low. China gonna come collect their debt? Lets not forget that china is also 5 trillion dollars in debt. Our economies are joined at the hip.
That being said, there is a war on the horizon. Time will only tell who it is with.