In short, it appears as though educational levels are the critical factor in predicting shifts in the vote between 2012 and 2016. You can come to that conclusion with a relatively simple analysis, like the one I've conducted above, or by using fancier methods. In a regression analysis at the county level, for instance, lower-income counties were no more likely to shift to Trump once you control for education levels.11 And although there's more work to be done, these conclusions also appear to hold if you examine the data at a more granular level, like by precinct or among individual voters in panel surveys.
But although this finding is clear in a statistical sense, that doesn't mean the interpretation of it is straightforward. It seems to me that there a number of competing hypotheses that are compatible with this evidence, some of which will be favored by conservatives and some by liberals:
- Education levels may be a proxy for cultural hegemony. Academia, the news media and the arts and entertainment sectors are increasingly dominated by people with a liberal, multicultural worldview, and jobs in these sectors also almost always require college degrees. Trump's campaign may have represented a backlash against these cultural elites.
- Educational attainment may be a better indicator of long-term economic well-being than household incomes. Unionized jobs in the auto industry often pay reasonably well even if they don't require college degrees, for instance, but they're also potentially at risk of being shipped overseas or automated.
- Education levels probably have some relationship with racial resentment, although the causality isn't clear. The act of having attended college itself may be important, insofar as colleges and universities are often more diverse places than students' hometowns. There's more research to be done on how exposure to racial minorities affected white voters. For instance, did white voters who live in counties with large Hispanic populations shift toward Clinton or toward Trump?
- Education levels have strong relationships with media-consumption habits, which may have been instrumental in deciding people's votes, especially given the overall decline in trust in the news media.
- Trump's approach to the campaign — relying on emotional appeals while glossing over policy details — may have resonated more among people with lower education levels as compared with Clinton's wonkier and more cerebral approach.
So data like this is really just a starting point for further research into the campaign. Nonetheless, the education gap is carving up the American electorate and toppling political coalitions that had been in place for many years.