One of the earliest uses of the term "politically correct" in the sense in which we currently understand it -- dogmatic language boundaries aimed at conforming to a political belief -- is found in a New York Times article from 1934. The title of the article makes its subject obvious: "Personal liberty vanishes in Reich."
The article describes the propaganda of Nazi Minister Joseph Goebbels and the crackdown on the rights of German Jews. The government controlled all means of communication to its own ends, including the press. "All journalists must have a permit to function," the Times reported, "and such permits are granted only to pure 'Aryans' whose opinions are politically correct." A warning follows: "Even after that they must watch their step." One editor published a critique of the government as he believed was encouraged by Goebbels, only to lose his job and be sent to a concentration camp.
"Political correctness," as you might have assumed, was born into politics, not adopted by it. Its transition into culture and back into politics -- as manifested by its prominence on the campaign trail -- makes sense once you consider the history.
After the fall of the Third Reich, the term was used in the same derogatory way to describe how the Soviet Union attempted to constrain its citizens. A 1949 Times report describes the need for reports in the daily Communist newspaper the Daily Worker to be "politically correct." Or, rather, "'politically' correct," using the Times' punctuation. The expression hadn't yet cemented into the two-word construction we recognize today; it was simply a way of describing a form of "correctness."
You can see the tiny uptick in use of the phrase as the Cold War progressed in this chart from Google looking at the use of it in books. Little to nothing until the end of World War II, then a little bit more in the 1970s -- and a veritable explosion thereafter.
By the mid-1980s, the Times was using the expression with more regularity -- and more casually. For example, a 1985 article about a record company in Hartford that had begun importing music from the USSR notes that "[c]urrently, jazz is politically correct in the Soviet Union."
A 1986 profile of a student named Jeffrey Vamos demonstrates as clearly as you can imagine the nascent overlap of the anti-Communist political use of "politically correct" with its cultural one. Vamos, who'd spent time in Leningrad through a program a few years earlier, describes how gender issues had become tense at his school, the Union Theological Seminary. (The article's author notes that, "[t]he feminist issue at Union is virulent. When it became known that a male student was to be the principal subject of this article, students protested to the administration.")
At the Christmas sing, for example, Jeffrey led his classmates in a rendition of his favorite carol, revised to the nonsexist "God Rest Ye Merry, Gentlefolk." But the obsession with the issue of nonexclusive language increasingly irks him.
"It avoids the issue," he says, "because if you're dealing with your sexuality in a political way you're not dealing with yourself as a person. There's too much emphasis on being P.C. - politically correct."
After graduation, Vamos planned to return to the Soviet Union.
By the 1990s, with the Soviet Union no more, the term had shifted almost entirely into the cultural context in which Vamos used it. It became much more widely used in the Times, for example, as it also became much more widely used elsewhere.
We can track it in a slightly hipper publication: Rolling Stone. In 1992, the magazine criticized R.E.M.'s Michael Stipe for suffering from "'man for all causes' syndrome," given that he wore "all those politically correct T-shirts on the MTV Video Music Awards show." Two years later, it was Evan Dando of The Lemonheads, who declared that, no, flirting was not politically incorrect. Liz Phair lamented that she failed her politically correct friends by "providing a refreshing, fascistic point of view to the conversation." And by 1998, Jack Nicholson was stipulating that political correctness shouldn't prompt us to cheer for a woman who cut off her husband's penis. (This was the Lorena Bobbitt era.)
This is the "politically correct" that we know and love/hate: An expression used to show our independence from the regimented thought that defines Communists and Nazis and R.E.M.
After its 1990s heyday, it bubbled under the surface until America's demographic and economic shifts led to renewed uncertainty and resentment between cultural groups. Fights over religious identity and gay marriage gave the term new life in recent years, and the deaths of several young black men at the hands of police increased racial tensions that some framed as being fights over political correctness.
It arrived back into the political conversation in style as the Republican presidential front-runner easily rebutted Megyn Kelly of Fox News when she asked about his past derogatory comments toward women. "I think the big problem this country has is being politically correct," Trump said, to loud applause. "I've been challenged by so many people, and I don't frankly have time for total political correctness."
In recent weeks, political correctness has been blamed for everything from terror attacks by the Islamic State (including five times during Tuesday night's debate, beyond Carson's usage) to Trump losing honorary positions in Scotland. It's evolved into something of a catch-all for the right, used to decry any number of things for any number of reasons.
The evolution, then, went like this. Political correctness was a standard of correctness applied by political institutions, which then became a dismissive way of referring to language-policing by non-political institutions, which then became a way of referring to disputes with political opponents. "Political correctness" is now largely a synonym for "the way the left does it."
Which, in a sense, is what it meant in the Cold War, too.