The guidelines provided by Congress are in regards to national security. Trump has taken that to mean that he can just say the words "national security" and issue whatever tariffs he wishes, even when he has publicly expressed motives other than national security. A lot of this has to do with the fact that he doesn't understand what trade deficits are. As for public interest: you overestimate how interested people are in Constitutional minutia. Most of the people I've had this discussion with were not even aware that taxes were a Constitution power until I brought it to their attention. Plus, the far left would LOVE to have this power when they take over, so of course they don't want to speak up too much about it.