The excellent web site 3Quarks Daily has a rather deep philosophical analysis of “post-truth politics” which I would recommend people study carefully.
One comment on this essay makes a further point.
Isn't it an old distinction that politics and deliberation are about things which could be otherwise than they are, and science and theory about things which cannot be otherwise than they are? If that is true, then, the real problem may be in bringing the concept of truth into the domain of politics, which is a domain of practical actions and decisions. That does not mean that anything goes in politics but only that truth is not the overarching parameter. For instance, insofar as we would want to make the issue of climate change an issue of truth (it is indeed happening, it will indeed hurt us), we are removing it from political debate.
So the real distinction may not be between truth and post-truth but between things about which we have some agreed-upon criteria for handling them (matters pertaining to science and truth) and things about which such criteria are not available. And, this distinction is itself not given but made and remade in the light of available knowledge.
The problem with this is that if we as a country (or many countries) decide to act (or neglect to act) in a way contrary to the truth of climate change because we do not accept the agreed-upon criteria for matters of fact, since we re doing “politics,” then this is bad politics. We have to be able to distinguish between bad and good politics.