My argument isn't based on the Commerce Clause at all. And I have to laugh at those that say that Congress could appoint someone to do the negotiation for them.
They already did. It's called the Commerce Department.
Unless you or anyone else here is prepared to argue that Congress cannot create agencies to carry out the laws which it has enacted, then you have no argument.
Congress has never vested a single individual with paramaters and authority by which to negotiate trade deals. The Commerce Department promotes trade but it has never had specific congressional authority to negotiate trade deals such as NAFTA. That's why we're having the TPA debate. Your rebuttal is bogus.