US & Russian participation on the International Space Station.

[Anomalocaris]

So the US would need to show it can continue to deliver more on each of the areas where China is striving to catch up and out do the US.    Ditching a nominally international space station would clearly not serve the greater national goal of power.

The Universe and even the Solar System are so vast that no nation will be able to explore everything, even if that is all that they did.  If China wants to be "first", so what!??

Also, another more subtle, but as sure as the sunset, evolution in the legal framework of space travel is the superficial bonhomie that existed since the dawn of space travel which proclaims space to belong to no one nation or private organization and to be a common patrimony of all mankind is slowly coming to an end.    We don’t want to perceive to be the one that ends it because of the optics, but we are certainly the one subtly driving the move to end it because for the moment our advantage in capability make it seems to us that we stand to benefit the most from its ending.   So gradually all solar system will not be free for all to explore.   Legal frameworks will be set up for nations and cooperations to cordon off parts of the solar system for exclusive economic benefit.   

To be able to assert this against China - the single nation most likely to possess both the capability and weight to contest our claims - the US needs to be seen as more desirable and reliable space partner by more nations than China.   So ditching ISS could potentially have more weight downstream consequences,