At WaPo Caitlin Gibson does us a service by tracing the history of the expression:
The phrase has become inescapable — again. In campaign speeches, media headlines and your Twitter feed: “politically correct.”
But what does it actually mean? Depends what year it is, and whom you’re asking.
These days, for GOP candidates, it’s a catch-all synonym for liberal cowardice or caution — whatever it is that’s keeping America from being great, or something. But “politically correct” is a linguistic weapon that has changed hands many times.
It’s been a literal term. An ironic joke. A snide insult. To some, the term has even represented a positive ideal, a righteous label worn proudly.
1932: “We looked over the program, but are sure that few farmers would ever understand it. Of course, it is politically ‘correct’ to the last letter.”
— Harrison George, a leader of the U.S. Communist Party, on its support for the United Farmers League in the Communist newspaper…By the early ’90s, more people were growing outraged by “political correctness” in higher education, and fewer activists were flying the “P.C.” banner as a glorified ideal. When the first President Bush declared that free speech was under siege by P.C. culture, “mainstream America [began] to latch onto this term,” Burnett says. “That’s when ‘political correctness’ appeared on the nightly news.”
More than 25 years later, you can still find it there. But instead of describing a culture clash within academia, it’s now a broad-brush insult directed against any ideological opponent.