To answer the question, while most nations are better off, and yes, trade is a positive sum, the geopolitical fact that China is a competitor with the US makes

To answer the question, while most nations are better off, and yes, trade is a positive sum, the geopolitical fact that China is a competitor with the US makes them an 'economic threat'. Rather, they're a political threat, and can wield any of the many tools a nation has to interact with one another, from military might, economic might, political influence, etc. That said, both nations are still better off working together.