'Post-truth' is a silly buzz word, and therefore beloved by journalists who typically talk and write uncritically in trendy ways. There is no way to get beyond truth or to live after truth. All of our intellectual operations are conducted under the aegis of truth.
Here is one example of how we presuppose truth. People routinely accuse each other of lying, and often the accusations are just. But to lie is to make a false statement with the intention of deceiving one's audience. A false statement is one that is not true. It follows that if there is no truth, then there are no lies. If we are beyond truth, then we are beyond lies as well. But of course lies are told, so truth exists.
I could squeeze a lot of philosophical juice out of this topic, and you hope I won't. I will content myself with some mundane observations.
'Post-truth' is used mainly to describe contemporary politics. The idea is that it does not much matter in the political sphere whether what is said is true so long as it is effective in swaying people this way or that. What is persuasive need not be true, and what is true need not be persuasive. But this has has always been the case, so why the need for 'post-truth'? Is it really so much worse these days?
For the Left, Donald Trump is the prime post-truther, the post-truth poster boy if you will, the prima Donald of the practice of post-truth. Ruth Marcus of the Washington Post doesn't expect him to truth up anytime soon. "Indeed, all signs are to the contrary — most glaringly Trump’s chock-full-of-lies tweet that 'I won the popular vote if you deduct the millions of people who voted illegally.' "
A very stupid example, Ms. Marcus! There is not even one lie in the tweet, let alone a bunch of them. Although verifiable in principle, Trump's tweet is unverifiable in practice. Trump had no solid evidence for the truth of his assertion. Still, it could be true. Don't forget the 'necro-vote' (a word I just coined) and the illegal vote. Trump's epistemic 'sin' was not that he stated what is not the case with the intention to deceive but that he confidently asserted something for which he had insufficient evidence. He pretended to know something he could not know. Very annoying, and possibly a violation of a Cliffordian ethics of belief, but not a lie.
So he didn't lie. What he did was close to what Harry Frankfurt defines as bullshitting in On Bullshit, a piece of close analysis, fine, not feculent, that was undoubtedly more often purchased than perused. The bullshitter doesn't care how things stand with reality. The liar, by contrast, must care: he must know (or at least attempt to know) how things are if he is to have any chance of deceiving his audience. Think of it this way: the bullshitter doesn't care whether he gets things right or gets them wrong; the liar cares to get them right so he can deceive you about them.
So you could fairly tax Trump in this instance with bullshitting. He shot his mouth off in a self-serving way without much concern over whether what he said is true. But why pick on Trump?
Because you are a leftist and thus a purveyor of double standards.
Obama bullshits with the best of them. A prime example was his outrageous claim that 99.9% of Muslims reject radical Islam. It is false and known to be false. (You can check with PEW research if you care to.) Now was Obama lying in this instance or bullshitting? A lie is not the same thing as a false statement. Let us be perhaps excessively charitable: Obama made a false statement but he had no intention of deceiving us because he did not know the truth. (Compare: G. W. Bush was wrong about the presence of WMDs in Iraq, but he did not lie about them: he was basing himself on the best intelligence sources he had at the time.)
But that Obama is pretty clearly bullshitting is shown by the cliched and falsely precise 99.9% figure. The whole context shows that Obama doesn't care whether what he is saying is true. He said it because it fits his narrative: Islam is a religion of peace; we are not in a religious war with Islam; Muslims want all the same things we want, blah, blah, ad nauseam. The difference between this case and the Trump tweet is that we know that Obama was wrong, whereas we don't know that Trump was wrong.
So once again we have a double standard. Trump is 'post-truth'; but Obama and Hillary are not?