Controlling for race, are suburbs different from what they once were?

[Del Tachi]

For comparison, DuPage County was almost 90% non-Hispanic White in 1980.  So it's both.  Yes, college-educated White voters have trended towards the Democrats (and massively so in certain suburbs around A-tier cities like Chicago, Philadelphia, etc.) but these same suburbs have also been getting more diverse.  I expect Democrats didn't outright win the White vote in places like DuPage, IL or Montgomery, PA until 2016 although those trends have been present since the late-80s/90s.  Clinton, Gore and Kerry actually managed to do very well in suburbs. 

I would note, too, that 1) college educated suburbs are much more college educated than they were 30-40 years ago, matching the overall trend towards higher educational attainment nationally.  The number of post-baccalaureate degree holders is also growing faster than the number of baccalaureate degree holders.  30 years ago, it would not be difficult to find a state school grad and his non-degreed wife living in Evanston or Winnetka...that's probably not very true anymore.  2) White college grads have gotten substantially more secular over the past 30-40 years.