Education and presidential approval

During the 2016 campaign, Donald Trump promised a large infrastructure program, major restrictions on international trade, and eliminating tax loopholes that benefited wealthy people.  As President, he's followed standard Republican economic policy--cut taxes and regulations on business and try to repeal the Affordable Care Act--and the "populist" elements have been pretty much forgotten.

Has the difference between promises and policies led to a change in the social composition of his support?  The Gallup Presidential Job Approval Center has more or less weekly data on presidential approval ratings broken down by various factors.  I calculated his average approval rates among people with and without a college degree in the first five surveys of his presidency (Jan-Feb) and the most recent five (Nov-Dec).  In the first five, his approval was 44.8% among people without a college degree and 36.6% among people with a college degree, for a difference of 8.2; in the last five, it was 38.4% and 32.0%, for a difference of 6.4.  That is, less educated people are still more likely to approve of Trump, although the gap may have closed a little.

I also looked at Obama's approval ratings among people with and without a college degree, using the first five surveys in his presidency, and then the last five in every year of his presidency (including 2009).  The results:

Obama's approval rating among more educated people relative to less educated people rose pretty steadily over his time in office.  At the beginning, he had only slightly higher approval ratings among college graduates (66% to 64%); by the end, it was a pretty large gap (61% to 53%).  It would be interesting to try to figure out the exact timing--was it a gradual shift or did it correspond to some events--but that would take more time than I can afford to spend on this. 

This does not mean that Trump is more popular than Obama was among people without a college degree:

His approval ratings among this group, even at the beginning of his presidency, were somewhat below Obama's average.  The striking difference in approval ratings between Trump and Obama is among people with a college degree.  

My tentative interpretation is that the differences in relative approval ratings are mostly about style rather than policy, or perceived policy.  More educated people are more likely to be concerned about standards of "presidential" behavior--less educated people may see violations of them as harmless or even as refreshing honesty. (See this post for a historical parallel)