I am pretty sure this is regards to BRICS and not about communists or how Brazil is governed. I get that it may not be the best nation politically, but USA didn't do anything about it, all the way until BRICS and now they are retaliating for what BRICS İs doing.

He already did this with Russia and China, now he is aiming at Brazil, and could even increase it more in the future. Dude knows that going to a war with any nation is costly and dangers his position, but making economical warfare is free for him and he is allowed to do. So instead of actually fighting, he is just increasing tariffs on whoever he wants, makes more sense to him and easier to handle the paperwork too, he doesn't get that much backlash because of it neither.