Canada

The US economy would crash without trade. That it would eventually recover to some stable but reduced state hardly matters.

Take aluminum and nickel as two examples. The US may theoretically have the resources required. But they do not produce enough and it would be years or even decades before they could. What happens to the auto industry or even their defence capability in the meantime? Other things, like Titanium, may not be available in quantity no matter how much time and money is spent trying.

Aluminum needs massive amounts of electricity. Where is that coming from? The US is a net electricity importer today. How long will it take to build that infrastructure?

How about microchips? How fast can you design all the chips you import? How fast can you build the fabs?

How long does it take to retrofit a refinery designed to process Canadian heavy crude? What is your energy output while those refineries are offline?

Even food is hard to pivot. Are Americans going to eat all those soy beans? And, as I heard someone else say “you cannot grow bananas in the US”.

When you say “comparatively poorer” I think it undersells the impact that full isolation would have by a massive margin.

For any other country, the impact of ceasing trade with the US can be offset by finding other trading partners. I stand by my statements.