A new study—which will doubtlessly be oversimplified and distorted by liberal blogs like us in order to demonize those whose political beliefs we find repulsive—has found that Democratic professors grade like this ("I am a laid-back hippie"), while Republican professors grade like this ("All the black students fail!").
What the study of professors at "an unnamed elite American university" actually found was that Republican professors tend to give more grades at the high and low extremes of the grading scale, while Democratic professors' grades tended to cluster in the middle, in a more copacetic manner. Oh, and this:
With regard to race of students, the study found that black students received lower grades, on average, than did white students whether classes were taught by Democrats or Republicans. In courses with Democratic professors, the gap was 0.27 on a grade point average. In Republican-led classrooms, the gap was 0.42.
The study's authors didn't say why Republicans gave harsher grades to black students, but the answer is "to give us something to argue about."