Two things:
1.) We are not going to be replaced as the top dog anytime in the near future. We always have the leverage to tell the other nation to piss off, with the other nation feeling as much, if not far more, pain than we feel from walking away.
2.) Other nations aren't likely going to play the !@#$ you game with us in the future, if we strike deals that are fair for both sides.
Trump isn't wrong that we have been taking the **** end of trade deals for decades, and that the other countries damn well know it.