James Galbraith in New Geography:
Using our measure of pay inequality, which avoids any distortion associated with making a conversion to income inequality measures, the fourteen states with the largest increases in inequality after 1990 without exception voted for Hillary Clinton.1 These fourteen included almost all of the large states that Clinton carried, including California, New York, New Jersey, Massachusetts, Virginia and Illinois. The largest Clinton state below the top fourteen is Washington, and after that, Minnesota (which she carried by whisker); the others include Vermont and Delaware, small states embedded in regions (New England, the Mid-Atlantic) where the increase of inequality was much larger than it was in the states themselves. Vermont is not immune from economic change in New York or Massachusetts, nor is Delaware unaffected by events in New Jersey or Maryland.
Conversely, the seven states with the smallest increase in inequality, and ten of the lowest twelve, all voted for Donald Trump. These included Wyoming, West Virginia, Oklahoma, Utah, North Dakota, Montana, Alaska, Indiana, Nebraska and Kentucky, as well as the critical Obama-to-Trump states of Ohio and Michigan. In the middle range, we find a series of states that were (or, in the case of Georgia, might have been) competitive including Wisconsin and Pennsylvania, Florida, and North Carolina.
The correspondence of inequality-change to the election outcome is almost uncanny.
A plausible explanation emerges with a moment's thought. Clinton-majority states are characterized by high-income enclaves of finance, technology, insurance and government contracts, which often exist alongside large low-income minority and immigrant communities, sufficiently separated by geography and political boundary lines to be almost autonomous from each other. Both of these communities vote Democratic, yet out of highly differing political and social interests; the former perhaps most of all for reasons of social liberalism and environmentalism; the latter out of economic interest and historical alliances on civil rights and immigration. Where they together predominate, Democrats prevail.