Who really understands the repercussions of all these tariffs?

The US tariffs on Canadian exports are hard to understand - both the theory and the practice.

For example, I read that "Canadian aluminum, steel products dealt biggest blow from US duties". But isn't aluminum and steel covered by CUSMA, and therefore exempt from the tariffs? Or is it just a small percentage of aluminum and steel exports that is actually being tariffed? Aluminum and steel are subject to tariffs at a different rate (50%), and with a different "justification" - does this, then, invalidate the CUSMA defence? Is steel and aluminum not covered by CUSMA? None of this clear to me.

On this last point, I think I have unearthed at least a partial explanation, but you really have to dig for it. The steel and aluminum stacked tariffs are a combination of "Section 232" sectoral tariffs (Section 232 of the US Trade and Expansion Act of 1962, that is) and additional tariffs under the International Emergency Economic Powers Act (IEEPA), both of which somehow escape the provisions of CUSMA, and can be applied regardless. Not that the US is actually in an international emergency economic situation, but that's another issue... So, essentially it is all done through legal smoke and mirrors: Trump's lawyers have been working overtime, finding obscure loopholes and applying debatable interpretations.

I read that between 80% and 90% of Canadian exports to the US are covered by The CUSMA agreement, and therefore exempt from the general 35% tariffs we are supposedly subject to (other than energy and potash sales, which attract a lower 10% tariff). I have seen figures of 86%, 90%, 95% - there does not seem to be a definitive figure. 

But also, that seems to be a theoretical figure anyway, and many businesses have never bothered with the onerous paperwork of proving that their products are CUSMA-compliant. So, the actual figure is probably a lot less, but no-one seems to really know. Many smaller companies that have never officially registered their products under CUSMA are now scrambling to do so, so the actual figure is probably something of a moving target. 

The latest figure I have read is that 81% of exports from Canada to the US are now CUSMA-compliant, up from 56% back in May. A Royal Bank of Canada estimate suggests that, because of CUSMA, the blanket 35% tariff the US now imposes on Canadian exports, is effectively reduced to about 6%.

This is all well and good while CUSMA is still a thing. It comes up for re-negotiation in 2026, and you can imagine how that is going to go. In the meantime, Canadian companies need to work dilligently to move their exports markets away from the USA.

I don't know whether Trump understands all this - maybe he's smarter than he seems - certainly he has a whole department keeping track of it all for him. But I have a suspicion that hardly anybody really understands it all in detail. The Canadian case may be more complicated than most, what with the CUSMA to take into account too. Presumably, somebody in the Canadian civil service understands it pretty well, and is keeping track of it. Me, I've just about given up.