BYD is going to set up in North America (like Tesla did). They can setup a factory in Mexico (where they are already selling cars?) just as easily as they can setup in Mississippi. I expect them to eventually setup in a car plant somewhere in an American southern state or Mexico. To avoid the tariff and for shipping reasons.
Japan used to make a lot of their USA-bound cars in Japan, even the cheap ones. I guess that is a difference between the 70s and today, though.
Assembling a car is < 1 days labour, so even if you're paying high north American labour rates, it's still cheaper than a spot on a ship from China.