True, the US can decide to exit a treaty. How likely is that, in this case? Not very.
TPP is not a real treaty, but it carries the force of a treaty.
Is the SCOTUS likely to find something unconstitutional? Again, it's true that SCOTUS could dump the TPP, but I think it's highly unlikely, given court's deference to intent of legislation, will of the legislators,etc etc.
The TPP just reeks not only of end-run around the will of the people, but manufactured consent as well.
I'm not trying to argue that the TPP isn't bad. It is. Nor am I trying to conceal the truth on anything regarding the mechanisms of government. I just wanted to state that there are ways to control the TPP should it get voted in.
The TPP isn't a real treaty as that requires a 2/3 vote in the Senate its what's known as a trade promotion authority.
Constitutional amendments trump treaties. If anything is found to be unconstitutional in the treaty by SCOTUS, then the treaty may need to be broken.