It is how tariffs/duties have always worked (paid by the USA importer at the USA point of entry)...and still work today. Mr. Trump knows this otherwise he would not have delayed tariffs on Christmas related items until after they have arrived in the USA:
https://cargofromchina.com/landed-cost/
Then why would the US Treasury be getting paid billions from China, if its the importers (US companies) that are paying them?