"The general premise of tariffs is that a foreign product costs e.g. $100 whereas a domestic product costs $120."

The analysis following seems to think that the tariff is placed upon the retail price of the goods as opposed to the production cost, which excludes marketing, final transportation, storage, r&d, domestic staff costs, profit, etc.

A more important aspect not mentioned is getting rid of the de minimis exemption that allowed people to ship stuff tariffs-- free into the US as long as they declared the value less than $750.