Why can't the US just steal the designs from China like China did from the US?
U.S. patents aren't valid in China, but Chinese patents are International.
That wouldn't solve their actual problem, which is that everyone involved in US car manufacturing could earn a similar amount of money doing something else, so they can't just copy the cost structure along with the design. On the other hand, making US-designed cars in China and importing them could work, but is unlikely to be politically palatable.