Justin W. replies, in part:
I’m skeptical that post-modernism had much to do with Trump’s victory. It is not even on the radar of most Trump voters, ...The main criticisms of Dennett seem to be that he wildly exaggerates the importance of philosophy and that he has misunderstood the philosophers in question. But I take him to be saying that postmodern philosophers, or perhaps merely the philosophers who gave rise to postmodernism, have done something that had very bad consequences. He isn't, that is to say, suggesting that Trump or the people behind Fox News have read Derrida, Foucault, or Lyotard and, based on a sound understanding of their work, become Thrasymachean liars. (If he is saying that then he has lost touch with reality.)
So what could he mean that might be true? Most people (in the US) don't study philosophy at all, either because they don't go to college (and philosophy isn't taught in high school or before) or else because they go to a college or university where philosophy is not mandatory. What philosophy they get--and enough people get some exposure to philosophy for opposition to philosophy to be part of the basis of a popular film--comes from other courses. In some educational systems this philosophy might be Thomism, or something like it, but more commonly I think it will be what I call postmodernism. I work in an English department and a high percentage of my friends teach in English departments at other schools. Postmodernism is common among these people. One even said that relativism, including the explicit rejection of belief in truth, was the basic dogma (they didn't use that word) of the discipline of rhetoric and composition. And almost every student studies composition, including in high school.
This is not the fault of Foucault et al., but they have a role to play in the history of the phenomenon. I don't know how ideas like postmodernism get into other subjects, but in English graduate students typically used to have to take a theory course (perhaps they still do) in which they would learn about various kinds of critical theory. I think these courses are often based on Terry Eagleton's book Literary Theory, on which Wikipedia is interesting:
Eagleton's approach to literary criticism remains firmly rooted in the Marxian tradition though he has also incorporated techniques and ideas from more recent modes of thought as structuralism, Lacanian analysis and deconstruction. [...]
After Theory (2003) represents a kind of about-face: an indictment of current cultural and literary theory, and what Eagleton regards as the bastardisation of both. [...] His indictment [...] centres on "relativism"...In other words, it looks as though Eagleton might be (in part) both the cause of and the insufficiently-used cure for the problem that Dennett complains about. I wouldn't blame Eagleton for this any more than I would blame Lacan, but it's a reminder that bastardisation happens and happens predictably. Bastardized versions of various kinds of philosophy (Dewey is frequently misquoted and misapplied too) are widespread. I blame the bastardizers first and foremost, but philosophers themselves could almost certainly do more to combat it.