They cannot unilaterally modify the deals, they might need the agreement of hundreds of other countries to change it. In return for their support, they will want concessions (like jobs) that exceed the ones we already made. That’s how it works, as thats what we do to them.
They try to trade jobs that are less profitable to do here. We are a great place for trade lawyers, and rocket scientists (as long as they are not unionized) but engineers, nurses, teachers, etc, they likely feel make too much.
I met one of these negotiators once, he went into length about how horrible it was, and how I really didn’t want to know what went on there, because he knew the effect of these deals were going to zap, pull the rug out from underneath lots of peoples entire lives, with the stroke of a pen. Something they absolutely don’t expect that nullifies their entire lives efforts in many cases (although it may take a few years for the changes to have their desired effects).