They are threatening China by saying "you will lose access to the american market. Everyone wants access to us. We have the highest buying power in the world!"
Except this party that is currently threatening them has spent the last 40+ years doing it's best to destroy that buying power by letting Americans go into severe medical debt before dying of preventable disease. Taking the side of big business to suppress wages and destroy unions. Allowing big business to destroy competition and limit choices down to over priced garbage, refusing to enforce laws on wage theft, refusing to enforce gun laws, refusing to allow black people to escape generational poverty, supporting job destroying AI technology, refusing to fund the social safety net so people can get jobs or at least use the welfare they get to contribute to the economy instead of dying on the street.
They're doing everything in their power to empower the rich who do not spend comparable amounts of money on comparable volumes of stuff. Jeff bezos isn't getting 15 million hair cuts every 2 weeks. Tim Cook isn't buying 8 million cars every month. Mark Zuckerberg isn't taking a flight every 15 minutes. Sundar Pichai isn't buying 10 million eggs every month. Joe rogan isn't buying 20 million t shirts.
The economy in America is at the mercy of people who are addicted to increasing their wealth not using it in a way that keeps businesses going. Their contribution to the economy is buying some luxury goods and services that only they can afford and then buying shares in companies producing things that a growing number of regular people cannot afford.
The chinese know this is bluster because unlike the people running the country now, the chinese leaders actually know how to read and have been watching America continue to abuse it's middle class and poor. Theyve watched America do the OPPOSITE of what China, korea, and Vietnam did(lift millions out of desperate poverty). Theyve watched as americas purchasing power parity has diminished. They understand that democracy requires an educated, healthy, informed population to function properly. The leaders that are elected represent the values and intelligence of the population.
Trump's election in 2016 confirmed their suspicions that the average american is a moron. His subsequent actions gave them motivation to continue to invest in their domestic industries because they knew there was a chance he'd be back in 2020. He wasn't, but that just gave them more time to prepare especially since Biden didn't change americas position on China and in fact doubled down on the hostility.