The president Does have this authority just like all the presidents before him who used these same exact laws.
Of course President's can enact tarrifs....
Wherever you get the idea he can't is not coming from the constitution. Because it most definitely spells out that it is him that can enact, raise, or lower them. He also sets the lease rates for docks and federal land leases used for oil production.
That's the executive branch....he doesn't just look pretty, sign bills into law, and ride around making speeches.
The man is busy WORKING 16 hour days....unlike Potato who barely did 4.