On the US being able to be defeated military by china, I doubt that will happen in this century. If it was a one-on-one fight, then maybe. But you have to take into account the US system of alliances. Lets see what other countries the US can rely on for support in the region:
Japan
Apparently after WW2, the Japanese “forever renounced war” as a means of settling disputes and disbanded its military. But during the korean war, it was realised that Japan should have an army to assist the US if any such future conflicts arise. Thus the JSDF was born. This army has grown and is now bigger than the armies of Britain and France COMBINED. It is also considered to be the finest fighting force in the region and ranked even higher than china. Japan, ON ITS OWN, would be a formidable foe for china. Also, Japan is considered a nuclear threshhold state, i.e. a country that can build weapons in a couple of months if she chooses: https://en.wikipedia.org/wiki/Nuclear_latency
India
Though not yet a full ally that would go to war if the US and China fight, its well known that these 2 countries are bitter rivals and the US has been cultivating India as a counter to china. India also knows that at the present time, she could never defeat china without uncle sams help so is essentially leaning towards uncle sam. India is another country that is expected to become a superpower in the coming decades and its population is expected to surpass china (if it hasnt already) sometime in the near future and uncle sam wants to make her a full ally.
Other countries in this region with powerful armies would be South Korea, Australia, Taiwan, Thailand who are all US allies.
And remember, these are just uncle sams allies in the Asia Pacific region. We havent talked about Europe or even Canada
Militarily, China still has a long way to go in order to defeat uncle Sam
On the economic front i.e. the current trade war with china, I dont see America winning this. She is severely hampered in this fight since she is a democracy whereas china is a dictatorship. China has been introducing sanctions that are designed to make trump loose support in a large number of states thus weakening his chances of reelection. If things get bad for the US, its just a matter of time before he is either impeached or voted out of office. China has no such considerations. Being a dictatorship, they can fight to the bitter end without worrying too much what the people think or by using propaganda, Goebbels style, to control the people.
A perfect example as to the way a dictatorship can fight to the bitter end is WW2, specifically the fight between USSR and Germany. Stalin would never have won that war with a democratic system of govt just as Germany would never have fought to a point where much of it was invaded and destroyed, including Berlin, if she was a democracy. In a dictatorship, you can do extreme things where as in a democracy, you cant.
America winning the trade war… Nope!