I was just thinking about how most people been hearing America is the number 1 country in the world since they were born. I don't know who the media will blame, but some will start stroking fear.
The average person might not care in the beginning, but once media, and politician starts making people fear I feel people are going to start looking for a "strong man" to save them.
Many average US citizens will probably turn to fascism.
My wild speculation:
When China overtakes the US, many will simply see it as an ethno-authoritarian state beating out liberal democracy. This is an incorrect characterization of China, but it's the line US media has been pushing.
Because of this mischaracterization of China, many will think that the US must become an explicitly ethno-authoritarian state to maintain "hegemony". In reality, the lesson they should learn is that they need to have an effective and trusted central government that can coordinate and discipline capital so that it can plan long term, and in a more pro-social way.
However, that is not in the interest of US capitalists. Their narrow, short-sighted interests would benefit much more from an increasingly authoritarian state (under their control) which justifies increasing tyranny using the idol of western chauvinism. Many US people will support this.
Edit: this is also one of the many reasons why we must organize and talk to people irl