I think it's interesting to analyse Xi, who unlike Trump is aware that the US is failing and that most likely China will dominate a future global economy, but who must by now be wondering what an inevitable decline looks like for China. Can he postpone it somehow? Are its seeds ultimately in something he will do, or worse has already done? That's not a happy thought is it?
Meanwhile the US's "supposed upcoming ending" puts them in a better position than the UK was in many different categories. It still has massive resources, amazing talent and a citizenry with an "ambitious" can do attitude vs the "tall poppy syndrome" of the UK. Its difficult to argue that there is an exact end date thats occurring now. To say its all over and that there isn't a second story coming seems premature.
Re China: This is a country that has overexpanded in infrastructure which will come home to roost sooner or later, has a terrible demographic structural collapse looming with no realistic way to correct(unlike the US which has options to correct), has overinvested in so many industries that they are experiencing massive (25%) youth unemployment with deflation occurring. They have serious problems coming in the next few decades.