I think we could be at a turning point. If trump carries out his insane policies, the US economy could be trashed, maybe he will try and create an oligarchy similar to russia. He may end up trashing NATO, breaking the democratic western alliance - just what russia and china want. This might be the clusterfark that ends the century of US dominance and starts the era of chinese dominance. Interesting times, for sure.
Maybe I'm being a bit too "glass half-full" but I'm hoping the rest of <whatever group> can now start to sort themselves out and move forward in a stable manner. The rest of the world has to step-up and can at least plan long term without the US pratting around participating ... oh no, pulling out ... participating again ... pulling out again - that's madness and just disrupts the way forward for everybody..
So (extended) Europe forms a new defensive alliance without the US - it will be smaller and weaker but still significant enough to achieve what's needed and at least it will be stable without everybody having to wonder if the US is still going to be helping in a few months ...
Pity the WHO wont have the US but rest of the world has to make up the budgetary difference and/or rationalise what the WHO does but at least we can be confident about it being stable for the long term without uncertainty about US. Shame US wont be opart of the "Pandemic Agreement" but then they wouldn't be acting on eg vaccination steps (at least not at the moment) so they'd have been an unreliable participant anyway.
Same with Paris Climate Agreement. Shame the US is planning to pollute the atmosphere and climate for the rest of us but if that's their attitude so-be-it and we'll have to do the best we can, endure the climate change impact (as they'll have to as well) but at least we can plan a way forward knowing where we stand without the Hokey Cokey (in, out, in, out, etc.). Rest of the world will form opinions about the US reliability and cooperation based on their actions.
Shame but they've chosen and we'll have to get on with it and let them shoot themselves in the foot, just like we in the UK did over Brexit.
Ian