ON THE USE OF THE TERM "POLITICAL CORRECTNESS"

Conservatives LOVE to claim that liberals invoke "political correctness" to stifle free speech and I've been curious about the history of the term.  In "Report of the subcommittee of the Joint legislative committee to investigate procedures and methods of allocating state moneys for public school purposes and subversive activities. (1942, New York State)" I found this reference:

to a Communist publication of 1935.  Based on my online searches, the spike in usage of the phrase by conservatives began sometime around 1990 and in 1991 Michael Kinsley wrote a column that poked some fun at the Right: "Hysteria Over 'Political Correctness': Where's this left-wing reign of terror on campus?", WaPo, May 3, 1991.