Aiken & Talisse go all post-truth.

Let us suppose I am a Trump supporter. Let us further suppose that I believe that many of Trump's statements are false but I still don't think Trump is a liar. 

Am I a 'post-truthist?'

Judge for yourself.

This is how I would respond to the following diatribe by a pair of Professors of Philosophy (My comments are in bold) 

In Philosophy, there is a familiar distinction between internal and external criticism.  In the real world there is a familiar distinction between Academic debate and stuff which actually means something . When a claim is criticized from an external perspective, the critic attempts to show that the claim fails to satisfy some criterion of success that he himself imposes. Why should he impose a criterion of success himself, instead of genuinely looking for the Schelling focal criteria likely to be consensual for all relevant readers of the text he is criticizing? After all, the critic wants to persuade others rather than just ride his own hobby horse to death without influencing anybody. In any case, David Lewis covered all this long ago. 

External critics hold their targets to standards supplied by the critic himself, external criticisms are commonly met with counter-charges of question-begging. An external critic of what you have written may denounce your writing as failing to hit the mark because it does not cause its readers to immediately apply for gender reassignment surgery- which is the only way we will get a truly equal Society. Here, the critic has himself supplied the standard by which you are to be assessed. Will you really combat this external critic by a counter-charge of question begging? Wouldn't it be safer and simpler to just giggle nervously and edge away from such an interlocutor? And this is surely the response to expect were one to offer an external criticism of post-truthism. To simply assert that indeed there are politics-free facts is to invite the counter-assertion that the very idea of a politics-free fact is itself a covert assertion of a political viewpoint, one that the post-truthist rejects. Oh dear! You think Trumpistas are exponents of Post Modernism. Joe the Plumber is constantly quoting Derrida to Jack the Dry Wall guy. Still, even if this were the case, so long as there is a Schelling focal criteria for the target audience which the author has not 'internalized', it remains the case that an external critic does have an Archimedian point from which to overturn whatever is persuasive in the 'post-truthist's' argument.

Let's take a concrete example-
Paul Gottfried has been described as the 'godfather of the alt-right'. His notion is that America is no longer a liberal democracy but rather a 'therapeutic managerial state' and that this works to the disadvantage of a particular coalition which Gottfried himself thinks is more worthy than any other and which probably excludes low IQ, monkey-god worshiping, darkies like me. 

I excerpt the following from an article on Gottfried in the Tablet-

'Today, we are ruled by a class of managers who dress like bureaucrats but act like priests. This technocratic clerisy justifies its status by enforcing Progressive precepts like multiculturalism and political correctness, which pit different groups against each other as if they were religious edicts. As Gottfried tells it he was banished from the mainstream of political discourse for rejecting this liberal catechism. Now, versions of the same ideas that Gottfried says got him banished will be gospel in Trump’s White House.'

This is not a philosophical but rather a socio-economic argument-  one which privileges a particular coalition in a manner adversarial to the existing 'core'. It can be formulated game theoretically and then empirical studies can be conducted o determine whether there really is some malign rent dissipation associated with this soi disant 'therapeutic managerial' clique.
Once some empirical work has been done, one can certainly have a sensible discussion about this- it just won't be a philosophical discussion except in so far as we hit open problems in Maths.

What remains, then, is internal criticism. The internal critic attempts to show that his opponent's view fails to satisfy some desideratum that the opponent herself embraces. Accordingly, the gold standard for internal criticism is self-defeat. That is, one ironclad mode of internal critique is to show that the opponent's view is inconsistent with itself. What if the opponent subscribes to Dialethia or multi valued logic or a particular kind of intuitionism? Then no scandal obtains. In any case, there's always problem of disentangling the quid juri/quid facti distinction so as to get clear of the Duhem-Quine thesis. 
 To get the flavor, imagine the simple-minded relativist who asserts that "no statement is objectively true." This claim is commonly offered as a critical maneuver against some proposed candidate for an objectively true statement. The trouble is that the simple-minded relativist's claim is self-defeating, as it itself purports to express an objective truth. It is simple-minded to suggest that it is objectively true that a self-defeating claim can be distinguished from any other sort for all possible affirmations of that claim unless all language is necessarily intensional. So if there is a version of relativism that is internally coherent (an open question in Philosophy), it can't be simple-minded.  Nor, by the same token, can there be any refutation of it which isn't simple-minded.
The trick for the sophisticated relativist is to figure out a way to deny objective truth while also preserving relativism's critical edge.
One way to preserve the 'critical edge' of a way of looking at the world, is to show that it generates propositions with some novel conceptual tie to a type of action which appeals to people on deontological, consequentialist, thymotic or virtue ethical grounds or some mix of such grounds.

A similar line of internal criticism can be launched against the post-truthist. Recall that those who embrace the post-truth phenomena tend to offer post-truthism as a critique of the status quo. As we saw, the denial that Trump's lying is objectionable substantially blunts the critical force of the claim that Hillary is "crooked." Not really. Trump has never held public office. The claim against Hillary is that she was a crook while paid by the taxpayer not to be so. We understand that it is one thing to 'blag one's way into a job' and another to commit a fraud once employed. It's a big theme in Hollywood movies and TV series and also in shows like the 'Apprentice'. The same goes for the tactic of denial; if Trump's unrelenting denials are exonerating, the same must go for any other persistent denier. Nope. Not if there is a Newcomb type dilemma in the one case but not the other. Tactics can only be judged against the broader strategic picture.  Mahatma Gandhi made a policy of pleading guilty to anything the British charged him with. Many Brits felt this, by itself, was 'exonerating'- a true seditionist wouldn't plead guilty to sedition; at the very least he would refuse to recognize the authority of the court.  Gandhi faced a Kavka Toxin type problem of a Socratic or Christ like nature and this was eventually the view that prevailed among the British establishment. Other revolutionaries, however, were not exonerated no matter what their plea.

 Insofar as these varieties of post-truthism affirm anything, they lose their critical edge.
Anything novel that is affirmed can only have a critical edge if it coincides with a Schelling focal point with respect to dissatisfaction with the status quo. One reason Kennedy got elected was because he banged on about an imaginary 'missile gap'. This tapped into a feeling of dissatisfaction prevalent at that time which saw Eisenhower and Nixon as small town hicks who didn't understand how quickly the Republic had grown into a Global Hegemon endowed with limitless technological prowess. Sputnik was small potatoes. The Nation wanted a guy who could promise a moon shot.

Matters differ somewhat with respect to the alternative media and intellectual nihilism. If anything, the difficulty here is more severe. "Alternative" news runs centrally on uncovering and publicizing the biases alleged to be driving the mainstream news media. But this activity draws its critical force from the tacit presupposition that news media are supposed to be unbiased. Nonsense! Nutters who think everybody in the Media is a homosexual Jewish Free Mason bought and paid for by the Rothschild Lizard People of Planet X don't want an unbiased news media at all. Nobody with any sort of axe to grind wants an unbiased Media or an unbiased Judge or an unbiased Umpire for that Tennis game in which I will smash the Williams sisters at Wimbledon and get the money for gender re-reassignment surgery. However, if post-truthism prevails, there is no such thing as unbiased reportage. Consequently, it's not clear what critical force there is in exposing the biases of a mainstream media outlet. To put the point in a different way, the practice of exposing bias derives its critical edge from the implicit claim that the exposing party is itself offering an unbiased objective assessment of its target.  Nope. It is enough to say that there is some alternative narrative which is more biased in favor of whichever in-group is being appealed to. But if the post-truthist holds that there is no unbiased perspective, then her perspective is simply another expression of bias. It is not clear how the clash of biases amounts to anyone being exposed or debunked. Actually, nothing could be clearer. In so far as the Media affects 'agenda control' and policy space is multidimensional, the McKelvey Chaos theorem predicts that rational agents will want biased Media, biased Representatives, biased Judges etc. What matters in any incomplete contract- including the Social Contract- is 'residuary control rights'. It is perfectly rational to seek a rent from the creation of a coalition which can be decisive if it acts cohesively to block or otherwise change the 'core' of the political game.
The same goes for the intellectually nihilistic version of post-truthism, since the view is supposed to be that those who think that there can be proper inquiry and evidence are either naïve or shills for the powerful. The view has its critical force in unmasking something that had been hidden. But if the nihilist is right, it itself cannot be in any better position to make such a critical point. Unless it is urging the capture of a rent- i.e. has a superior instrumental value.

And there's ultimately the rub. Although frequently presented as a means for speaking truth to power, cutting elites down to size, and shredding the pieties and practices that serve the interests of Washington politicians, post-truth politics ultimately has no critical force at all. 
You say the term 'post truth politics' was invented by left liberals angry and bewildered at Trump's triumph as an explanation of how such an improbable event had come about. Surely that means, if  the term has a non paranoid acceptation, it does have 'critical force'? After all, Hillary was a Washington politician. Trump was and always has been a private citizen. Even now, he and his supporters have made certain gains, though he hasn't yet become a Washington politician. So, this 'post truth politics' turns out to have actually changed something very visibly in the real world. A non politician, a non public servant, has been elected to the highest office in the land for the first time in History. Was there really no 'critical force' at work here?


Or, rather, it renders us all defenseless against the will of whoever happens to have power.

Really? When Trump becomes President, we will all be defenseless against his will coz of 'post-truthism'? OMG, what if he wants us all to turn into leggy East European blondes! Lucky I've kept my Margaret Thatcher wig from my student days...

Oh! Sorry, I was being dense. This article is just an exercise in 'post-truthism'. Gee, you guys sure gave me a scare!