Prove it. Just because he believed that Congress would never approve anything negotiated by Commander Xero and wants the next President to have that authority is not a sellout. It may be an error in judgment (considering Ryan and McConnell) but it is not prima faceae evidence of his intent.
The intent was to give the president absolute autonomy to negotiate the trade "treaty" that would normally require a two thirds vote of approval to become law. Now they must have a veto proof margin to kill it.
This was an insane deal, it gave Obama carte blanche to make the deal and the republicans in the Senate can't stop it.