Con law question - Fast-track Trade Authority

As I understand it, “Fast-track” trade authority (now called Trade Promotion Authority (TPA)), means that Congress voluntarily gives up the right to amend a trade agreement made by the Prez, reserving only the right to accept the deal or reject it in toto.
My question is: why would Congress have the right to amend a trade deal in the first place? Why aren’t trade deals considered treaties, which Congress has no right to amend? Is it because of Congress’ authority to regulate commerce?

Sua

Yes, and not just interstate commerce. From Article I, section 8 of the Constitution:

Bolding added, obviously. Treaties, back then, were mostly more of the “I’ve got your back if you get invaded” variety.

Thanks, manny. And, as I know you’re just drooling at the bit, I have no objection to closing this thread. :smiley:

Sua