Many are, but he is the President and it’s hard to stop him.
For one thing, rich people can benefit enormously from trade barriers. A trade barrier can be very bad for the economy as a whole, but really, really good for one company. A U.S. company that produces hot and cold rolled steel could make a lot of money from steel tariffs, even though the benefit they will get is less than the penalty other Americans will pay.
To use the milk tariff nonsense as an example, do you know who’s hurt the most by Canadian milk tariffs? Canadians. Because the Canadian government protects the Canadian dairy producer from competition, Canadians pay exorbitant prices for a limited selection of milk products. The dairy industry, however, makes out like bandits; being a dairy farmer can be insanely profitable in Canada because the government doesn’t let you fail, and forces consumers to pay too much for your milk. Dairy farmers will vote and lobby as a bloc in the limited number of electoral districts they’re numerous in and so have an outsides political influence, whereas the 35,000,000 Canadian customers getting screwed by this don’t vote as a bloc about this issue. The USA is the same thing; Wisconsin produces more dairy than all of Canada, so Wisconsin politicians are heavily in the pocket of that industry.
The benefits of free trade are enormous, but they are very much spread around. A tariff or some other protectionist racket is damaging but it usually helps a small, specific group of people while hurting everyone else a little bit. Budget Player Cadet said this very succinctly, as usual.
This is why these deals are hard for democracies to make and why Trump’s off the cuff “no tariffs no barriers” comment was stupid and not really serious. It takes a lot of time an effort to negotiate these things and make them work because every country has a few things it just cannot give up, for internal political reasons, and it’s different from country to country. If Canada and Germany wanted a bilateral trade deal, Germany would probably have to accept Canadian dairy protections, and Canada would have to accept Germany shielding its bratwurst or Panzer industry or whatever the hell Germans do. Both would be economically better off if they dropped that crap and eventually they might, but you take it as far as you can.
You also have to be mindful that humans are affected by this. As a Canadian I want our dairy industry’s protections taken away; they’re a giant scam. But simply ending them tomorrow would be a catastrophe for the real human beings who own dairy farms. People would go bankrupt and lose their homes. A few people would literally kill themselves, quite possibly. I can wait a few years to get cheaper cheese. The change needs to be gradual, negotiated, and phased in over years.