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:
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)