hey, screw you, some of us were history majors who realized we had to go to law school 
Haha, definitely not hating on those folks - some of them are my closest friends. I'm simply pointing out that maybe that is a more reasonable explanation for voters getting more Republican as their education increases but then sharply turning Democratic after a master's is thrown in.
To be fair, I feel like a big reason as to why Republicans lead so much among the some college and grad categories has a bit more to do with the makeup of the electorate than with anything else. While Republicans do tend to either lead just slightly College grads, and the Democrats consistently lead among Postgraduate students (as you said), I feel like it ultimately comes down more to how the election goes and demographics than anything else. In 2006 and 2008, both good Dem years, Democrats won every educational level category, with the exception of a tie among College Graduates in 2006 (Democrats won college grads outright in 2008). In 2010 and 2014, Republicans did well among most brackets, only losing out on those that didn't finish High School and the Post Graduates (again, as you said). In 2004, a close win for the Republicans, Bush lost the no High School category by 1% point, carrying every other category until the Postgrad level. Conversely, Obama in 2012 won every category (winning the some college category by 1% point) except college grads, which he only lost by 2% points.
So ultimately I think it has more to do with how the electorate looks than anything else. In a close election, the results tend to be narrow, and when it isn't close, not so much. Income really appears to be the same. Granted, we all pretty much know the wealthy trend Republican and the poor Democrats, but exit polls from 2006 had Democrats carrying every category up to and including 75k-100k, losing 100k-200k by 4 points and the 200k+ by 8. In 2004, Bush carried most every bracket by decent margins, losing the 30-50K by a single point.
As to whether or not Walker not having a college degree matters, I don't think it will. I wouldn't vote for Walker, but the fact he doesn't have a college degree has nothing to do with it.
