Now, that wasn't a view that was largely held on the right. In fact, I suspect it still isn't. The "post truth" on the right are people who still believe in truth, believe that they have it, and won't listen to any evidence to the contrary. In fact, maybe this is the consequence of the "post truth" left - if the right believes that the left believes what the left says about speech, then the right has no reason to trust any truth claim coming from the left.
But the change may in fact be as you say, that the post-truth people grew on the right. Now you can't sway chunks of either side with facts.