We have no lessons to learn from totalitarian regimes. I'm not saying protectionism didn't have bad or even catastrophic effects for those countries, I'm just saying we have no way of knowing for sure when there were so many other factors involved.
We've also never seen a dominant world power like the United States adopt mercantilism-ish style practices in modern times*. The United States is the economic engine of the world, and I say that as a non-american. I'm quite convinced smaller countries do self-harm by imposing tariffs. I'm less convinced when it is done by a nation that is to a large extent self-sufficient already, and demonstrably quite capable of running rings around the rest of the world when it comes to industriousness and innovation. A USA with an internal free market system and an external restricted market might very well function just fine. I'm less sure it'll work out very well for the rest of us.
*Not counting China, which has never quite been on the level of the US. But regardless, by and large their protectionistic practices served them well for decades.