Propaganda Free:
China makes most the world's aluminum. They make 10 times as much as Canada. Aluminum is a global commodity.
US aluminum production started falling in 1980 then sharply since 2000 due to our own mismanagement of our industrial assets. We will lose the ability to create aluminum in 5-10 years unless something changes quick.
Aluminum requires cheap power. The US decided cheap power sucks without realizing it was critical for defense materials. Our bad.
China uses coal to make aluminum for the US.
Steel? Canada doesn't make much steel, about 1/6th what the US does. China again makes most the world's steel. They make 10 times as much as the US, who used the be the world leader. While we are not at risk of losing what little production we have left, we are giving China a massive advantage in manufacturing since steel is the cheapest metal to build with.
The US defense industries import their steel and aluminum from potentially hostile China. China is building it's military up, and acting in an imperialist fashion as of today. This was not true in 2000 when we imported mostly from allies.
That's the situation. Canada is caught in the crossfire of the US's lousy policies from decades ago that we are finally paying for.
Is the US President an idiot? No. His job is to make sure the US is still around in 20 years. To ignore our poorly managed foreign trade agreements like past administrations have is suicidal.