>>>By relocating the remainder of their business south of the border, won’t a tariff be imposed on their product?
No. The administration has tended to increase tariffs on raw materials and intermediate goods, like steel and aluminum. It has chosen to avoid tariffs on final goods. So domestic producers face higher costs while producers in China and Mexico are able to get their end product in tariff free.
Why an across the board baseline tariff needs to be in place soon.
FYI there is now a tariff on fabricated structural steel products along with raw material. Mexico is the the largest importer. About 500,000 tons/yr.