I think the mistake you're making is that the protectionist policies of (say) the US and China are not remotely comparable. In particular, the whole reason the US needs steel and aluminium tariffs is that China has used protectionism and state subsidies to build a steel and aluminium industry so far in excess of what the country consumes that the surplus has tanked global prices. This is pretty much unprecidented. The US is not the only country that objects to this; the EU wanted to put tariffs on China a few years earlier but they couldn't agree on which goods the tariffs should apply to.

They do it because the people who vote for them eat it up. Politics is basically the "science" of hypocrisy. All you need is an easily impressionable audience, ideally with plenty of preconceived notions.

https://i.redd.it/gye28fevde011.jpg

Your analysis of American politics makes it sound like the entire voting block of US adults supports these policies, wanted this man as president, and watches Fox News. Fact of the matter is 3 million more people voted for the other candidate but this guy won on a technicality. The majority of Americans do not support these policies but our representative election processes are designed to prevent simple majority rule. Couple this with a legislative branch that cedes authority to the executive over the course of decades in the name of political expedience and we are where we are today.

I would argue that nowadays it could be framed as a "minority of Americans". [1]

1. https://www.nytimes.com/2019/08/07/upshot/trump-approval-rat...