The US is leading noone if nobody follows. Who do you think will follow?

Thousands of treaties, conventions, agreements, and other arrangements are negotiated all the time. The Paris accord is just one, but a major one. The belief that the American government can be trusted to stick to a good cause, let alone stick to deals it has made before, has been eroded. American diplomats will find it harder to persuade other governments to do anything. They will also find that they have fewer favours to call.