Comment by GeneralMayhem

As found elsewhere on this thread, the rate is based on trade deficit. Trump believes that having a negative trade balance with a country means that they're cheating somehow, as opposed to meaning that you just buy a lot of manufactured or raw goods for them.

And no, that does not make any sense, and you're not missing anything. He believes this because he's a fucking idiot. He's aggressively racist, comically petty and thin-skinned, and overtly authoritarian, and as far as I can tell actively wants to permanently destroy American science and civil society out of spite, but he's also really, really, really dumb. In this case, he's managed to combine his powers to take a goal that's born out of racism and xenophobia and then implement it in the most idiotic way possible, and somehow the result is even worse than the sum of its components.