Maybe they can't be revoked constitutionally, but there is nothing to stop a president ignoring the constitution even if it would result in serious repercussions: eg ordering internment outside due legal process, and the total breakdown of aw and order, where someone pardoned with just cause can be rearrested. Doing the right thing does border upon fascism, but if Americans don't want to live in a fascist state, they should have thought about the consequences before voting for trump.

regarding pulling out of the Paris accord, the rest of the world MUST take measures to mitigate US's additional carbon footprint, even if it means rationing energy.

Regarding WHO, if Americans do not want to be prepared for the next pandemic, that is their problem.