The shrinking of the middle is largely due to a recent rise in the share of women (who also represent a majority of college students) who identify as either liberal or far left. The share of female respondents, but not male respondents, who describe their political views this way was at an all-time high (41.1 percent for women, 28.9 percent for men). Left-wing views peaked for men way back in 1971, at 43.6 percent.
That is from the always interesting Catherine Rampell. The “political gender gap” across men and women, in these numbers, never has been higher, see the link for a picture and details but by one measure it is 12.2 percentage points.
Given the distribution of the “political correctness movement” across majors, how much it is simply the result of the increased feminization of education itself?