There are no winners in trade wars.

Persuasion research has clearly shown that the path to successful negotiations starts with getting to know the person you are negotiating with and identifying similarities between you before you begin.

Participants who skipped this step were successful 55% of the time; while participants who took the time to establish common ground before starting negotiations were successful 90% of the time and the outcomes of those negotiations were 18% better.  (Cialdini, 2017)

Because, people prefer to say yes to people they like. And they like people who are similar to them, cooperate with them, and pay them compliments.  Umm.  Are you starting to see the problem with Trump's approach to negotiations?

If you prefer history to research then consider the Smoot-Hawley tariff, which Herbert Hoover signed in 1930.  It led to a 66% decline in world trade, increasing the negative effects of the Great Depression.  (Nino, 2018)

As they say, those who don't study history are doomed to repeat it.

Cialdini, R. & Martin, S. (2017, June 8)  The Science of Persuasion.  Retrieved August 21, 2019, from

https://www.youtube.com/watch?v=kv0sOX6Alrk

Nino, J. (2018, March 11)  Tariffs: A History of Repeated Failure.  American Institute for Economic Research.  Retrieved August 21, 2019, from  https://www.aier.org/article/tariffs-history-repeated-failure