You think our defense budget will increase in the coming years? The way things are bjp might spend what ever it can get its hands on the economy than defense.In case we go to war with China, and it lasts a long time, what we need from the US (and Japan and other allies) is diplomatic support, intelligence, material aid/logistics support, financial aid and large scale investments. Nothing else.
Diplomatic and intelligence goes without saying. Material aid and logistics support are needed to alleviate stress from our own industry in order to counter accidents, delays etc. Financial aid is needed in order to support our forex, which will be needed to import equipment, without stressing out our regular forex income. Large scale investments are needed to counter the diversion of domestic investment towards the war effort in order to keep our economy going.
With the exception of diplomatic and intelligence support, the need for which is perpetual even for the strongest countries, we need support in the areas I mentioned until we become as rich as China is today.
Material aid/logistics support and financial aid comes at a cost to the US and allies, but investment is for mutual benefit. But if you consider we are fighting China, it would mean other countries are less stressed elsewhere, so paying us for the effort in order to keep it going is also in their favour.
We most definitely do not need American troops on our soil, never mind the fact that they won't send any in the first place.