Interesting thought. If you had more colleges per capita, would you necessarily have more professors per capita? Perhaps the count of colleges is not 1:1 with the count of professors (some colleges may be small).

I think that it is likely that there is an amplifying factor outside politics, which is that (in my estimation and experience) highly educated people are more likely to have advanced degrees. I know that sounds self-explanatory, but it's a compounding effect. For example, the more high school graduates you have, the more college graduates you have, and the more college graduates you have, the more advanced degrees you award.

So, having good basic education is going to lead to a higher number of advanced degrees awarded at the end of that cycle.

I think that rather than the "Democrat = Smart" story, this is telling a story of economic differences that goes back to the fundamental differences between the states. This is a story of rural vs urban. The more urban a state is, the more white collar jobs it has. And, it may be that the Democratic perspective resonates more with people in those jobs - that their policy ideas and values more align with urbanites.

I think if you were to do another graph with advanced degrees plotted against percent of population living in an urban environment, you'd find a strong correlation, and we may find that urban population is a better predictor of D-ticket votes than educational attainment.

Did a quick Google search and found this: https://engaging-data.com/election-population-density/

Being closely packed in with other people makes you far more likely to vote Democrat. (Unless you live in Staten Island, apparently. What a strange outlier. I don't know enough about NYC to explain this.)