From Nate Cohn’s Upshot column, which now has the most detailed data analysis on the voting patterns in the 2016 election:
Instead, it’s clear that large numbers of white, working-class voters shifted from the Democrats to Mr. Trump. Over all, almost one in four of President Obama’s 2012 white working-class supporters defected from the Democrats in 2016, either supporting Mr. Trump or voting for a third-party candidate. . . .
If turnout played only a modest role in Mr. Trump’s victory, then the big driver of his gains was persuasion: He flipped millions of white working-class Obama supporters to his side.
The voter file data makes it impossible to avoid this conclusion. It’s not just that the electorate looks far too Democratic. In many cases, turnout cannot explain Mrs. Clinton’s losses.
I continue to believe that the best account explaining these patterns is Katherine Cramer’s book, The Politics of Resentment: Rural Consciousness in Wisconsin and the Rise of Scott Walker. Though the book was written before the 2016 election and focuses only on Wisconsin, it documents the dynamics leading a substantial number of voters outside the major cities to being willing to vote for Obama (in both the 2007 primary and the general elections), Scott Walker, and Bernie Sanders. Obama had a strong enough appeal to these voters to carry enough of them to win the elections; as Nate Cohn’s analysis confirms, the primary factor accounting for the changed outcome in 2016 is that around 20-25% of white-working class Obama voters shifted to Trump.