There is a thing that I don't understand. Some years ago I remember Apple or Barak Obama stated that Apple couldn't move factories from China to other country because Chinese laborers were highly qualified, efficient and fast. So, I don't really understand, if America is so dependent on China, why does China heavily invests in U.S. Treasury bonds and makes its own currency weak to keep low export fees? It could profit more if the USA is really dependent on China.
They "buy US debt" and keep their exchange rate low because they want to force US to be dependent on China. If we look at the history, like the past 40-50 years we have a very weak country with no economy to speak of and no production while the population is enormous (about 850 million) and 85% of them are living in absolute poverty. That is 720+ million people who had literary nothing.
40-50 years ago there were two powers the US and USSR and they were fighting. China took advantage and created that dependence, slowly but surely. That way they grew. US also had no choice but to give China all these benefits, from technologies to investment. Otherwise the communists China would have played a 100% USSR favored game.
But at some point US regime realized while they were busy trying to destroy their competitor USSR, China had been growing too much and US was already heavily depending on China.
Now here is the thing, this used to be China's strategy to grow. Today almost all countries have lots of relations with China so China no longer "needs" US like before. At the same time when US publicly announces that China's economic growth is a threat to US national security (ignore how absurd that is) they are in fact declaring war on China. So China also retaliates by screwing US, for example they dump $175 billion of the US bonds they were bag-holding, they join the dedollarisation wagon, they respond to the tariff war with tariff of their own, they disrupt exporting goods to US to disrupt their market, they manipulate the energy market to keep the prices up and damage US economy, they reduce or stop export of raw materials, and a lot more...
And there is another thing that I personally think is a huge bullshit. Why doesn't America produces goods in the USA? Labor is expensive? Then they shouldn't produce food, shouldn't provide postal service, shouldn't do tons of thing if we think that way. And labor isn't that cheap in China too. I think they are just exploiting their employees and they wont' be able to do the same in the USA. Or may be? Idk, I have heard that Amazon exploits its warehouse and delivery employees too.
It is super expensive to produce almost everything inside US because it is a capitalist democracy.
Certain things like food is a different matter, because US is massive and has lots of fertile land for farming so it is still possible to do domestically not to mention that food is considered a strategic good so there is no way in hell they'd let US be fully depended on another country for that.
Other things like "postal service" that you mentioned are "services" not products and sometimes they can not be outsourced, they have to remain domestic.
With products like a phone, there is always competition. If you manufacture a phone inside US and have to sell it for $5000 while China manufactures the same exact thing but for $500 you simply can not compete and nobody is going to buy the $5000 domestic phone! Not to mention that they won't even be able to afford to pay that much even if there were no alternative!!!