Democracies change their mind. Big update! You should write a international relations paper on this.

Everybody understand that a treaty like Paris is just a big PR thing. Its is unenforced and the waste majority of people working on it will not be around when the results of it are in.

This is all about signalling. Trump wants to signal that he doesn't give a fuck and he is tough (or something).

If they wanted to know that American diplomacy is not consistent they could have looked at literally any point in US history. The could call Cuba what happened with the Platt Amendment.