They were not prepared and at least had to mitigate immediate harm, while preparing their economies, security, etc. to be less entangled with the US.

But once they are 'prepared' as best they can, one approach is for other countries to decide / accept that the US is mostly a lost cause while Trump or most other Republicans are in power, which will happen at times. It will affect their economies but they cannot control that. Negotiating with the US only encourages more bad behavior.

The rest of the world could then recreate (or continue) the global trading system, including the WTO, simply excluding countries that violate its rules. This puts the ball in the US's court to participate or not, never slamming the door in the US's face, always welcoming and encouraging them rhetorically, by their rules, and genuinely ('we look forward to our friends in the US joining and enjoying the benefits of doing business with the rest of the world').

In the meantime, global trade rules would be created in the interests of the other countries, without the US having a voice - a great boon after decades of US domination of such rules. This incentivizes the US to join sooner rather than later.

(It seems to me - I have no expertise in this area.)