Question: if you are a Republican, would you rather have a 68-20 lead among under-educated white people or among educated white people? Even if it is a smaller demographic, I'd rather have the educated whites. Educated white people can convince under-educated white people and can assuage concerns of minorities. Under-educated white people can convince only each other. They don't get much respect from ethnic or racial minorities. If anything, educated white voters might be able to make cogent reasons for not voting for Donald Trump -- and convince erstwhile Trump supporters that he will disappoint them.* Donald Trump, by doing so badly among educated white people by the standard of any Republican since Goldwater, practically ensures that such support as he now gets is all that he gets.
*My line? Some of the first decisions by Donald Trump will be which promises must he must break.
Gee, you must be a very educated man.