It’s active hostility to higher education from those on the right, because once you’re college educated, you tend to be more left leaning.

https://www.pewresearch.org/politics/2016/04/26/a-wider-ideological-gap-between-more-and-less-educated-adults/

"Highly educated adults – particularly those who have attended graduate school – are far more likely than those with less education to take predominantly liberal positions across a range of political values. And these differences have increased over the past two decades.

More than half of those with postgraduate experience (54%) have either consistently liberal political values (31%) or mostly liberal values (23%), based on an analysis of their opinions about the role and performance of government, social issues, the environment and other topics. Fewer than half as many postgrads – roughly 12% of the public in 2015– have either consistently conservative (10%) or mostly conservative (14%) values. About one-in-five (22%) express a mix of liberal and conservative opinions."