Congress gets to determine taxation on interstate commerce.
Correct. And the President isn't even allowed to broach the topic?
I seriously doubt that the President will be usurping Congressional taxation powers, inasmuch as the entire Democrat minority—as well as the GOPe majority— are looking for any chance to claim he's exceeding his Constitutional bounds.
After all, isn't the thesis around here that Congress wants to weaken this Swamp-draining President every way they can?