The United States, during the Nixon years, has opened the opportunity to China, because of their development of supply chains, to become competitive in the modern, contemporary world. That was welcomed both in China, as a way to play catch up with the West, and to enable Western plants and industries to get rid of what has become passe methods and take on the most advanced methods being currently developed at computer centers, now including those in the East--China, Taiwan, Japan and Australia, etc.--i.e., GLOBALLY.
Retooling was anticipated years and years ago by those who established the computer revolution, the culmination of which is embodied in Artificial Intelligence Research and its practical applications, being developed right now.
Retooling represents changes in industry but is also a cultural phenomenon: witness how "dated" some shopping malls are even today, each one virtually time-stamped as to decade by when each was considered "contemporary." Look at downtown Houston's vacancy list!
Whereas retooling took a long time years ago, today--once a capitol source is involved, the process can start to reconstruct a factory. Not that long. But it is naive for business to think it can prosper without having control of the business from its very inception and dedication of the property to be the headquarters of the enterprise to its finished product, linked by supply chains.
Now then, President Trump is saying that the United States ought to be significantly in with other countries where a finished product is distributed and sold. The issue of fairness arises as to where a process was performed by workers at a specific address within a locale of a particular country: It should be determined the cost of the process to be meted out as an expense, per process' evaluation. I take it he is also claiming that United States has not received for the company processes in making and selling the finished item performed at the company's locations due or equitable compensation, which includes profit and wages, at locations in the United States, where the process was performed. The government's take for providing services to enable the company to conduct its business at the address within the boundaries of the United States is within the scope of assessing the tariff charged at port of entry where the product is to be sold.
The issue of amount to be charged as a tariff is particular glaring in respect to agriculture. France, for example, highly prizes its wines, though other countries today may produce just as comparable wines, in the estimation of the consumer, as the French. Someone of Trump's persuasion, e.g., living in the United States might claim that Napa Wines are of similar quality; and may object to being charged more for French wines. That's the rub! The United States as importer determines the amount of the tariff the consumer must pay.
President Trump uses the tariff mechanism to bring about parity of wines, despite that farmers of France and farmers of California may loudly and vociferously disagree. It is the so-called "reciprocity of tariff."
My interpretation of President's fundamental argument (in my opinion).