I know for a fact the US government does not treat Canadian imports with partial foreign sourcing the same way.
NAFTA, like most of these agreements, is thousands of pages of special favors for companies big enough to own and operate their own politicians. It's very hard for smaller players to gain any benefits from it.
The theory NAFTA and TPP would make imports cheaper for the American consumer was quiet true, however with all the jobs lost due to this who has the money to buy the cheap crap? Chicken and egg...
With trade America first the world second, we win, they lose.