One of the strange things about the last year in Western political debate is how rarely the name of the departed philosopher Michel Foucault came up — and not for want of opportunity. One of Foucault’s key concepts, “biopolitics,” an account of the way that modern state power involves itself in the biological life of its citizens, was amply illustrated by the various governmental responses to the Covid-19 pandemic. The left-wing academic culture in which his work has long been dominant suddenly found its own influence extending all the way to corporate boardrooms and the halls of the C.I.A. A new volume of his work was published in English: “Confessions of the Flesh,” an exegesis of early Christian sexual morality.

There was even a Foucault scandal, an accusation that he paid for sex with Tunisian boys in the 1960s — just the sort of claim, you might think, that would prompt a pan-ideological debate about whether the shaven-skulled icon of postmodernism should face some sort of cancellation.

But when I search the pages of this newspaper (a decent barometer of prominence and influence) for the past 12 months, Foucault’s ideas and scandals merited at most a passing mention here and there. On Google Scholar, a different sort of barometer of influence, his citations actually dropped modestly in 2020. In debates about lockdowns, quarantines and other subjects associated with his historical and philosophical work, he was largely absent from liberal and left-wing discourse. You were more likely to hear his ideas invoked in conservative arguments, cited with a strange right-wing respect.

The place of Foucault in 2021 is not just a matter of academic interest; his changing position tells us a great deal about recent evolutions of both the left and the right. The best guide to this change is a New York University lecturer named Geoff Shullenberger, who has written a pair of essays exploring the political valence of Foucauldian ideas. They are best read in reverse chronological order: Start with his long piece in the latest issue of American Affairs, “How We Forgot Foucault,” which takes up the philosopher’s peculiar absence from the pandemic debates, and then turn to his earlier essay, “Theorycels in Trumpworld,” on the flowering of postmodern theories and themes among Trumpist figures on the right….