People trade in USD because the US is the largest of large economies. Everyone trading in USD understands already that the US can manipulate its own currency. But they take a low-risk bet that it probably would have far less incentive or inclination to do so than an authoritarian state like China or a small economy like Argentina. Capital flows to the US because the dollar has been "safe"... it inflates, but predictably slower. The Chinese regime is more than capable of opening the illusion of free markets and making 50-year promises not to interfere with free trade and capital, tempting foreign investment, only to break those promises with an iron fist.

Regardless of the response from China, America is showing that it is irrationally willing to cede its incredible advantage for no decipherable reason beyond that some logarithmic curve of population idiocy has crossed the already absurd hockey stick of its own national wealth. It's a realtime lesson in the ancient rule dating back to the fertile crescent, that civilizations destroy themselves from within before they're conquered from without.