Why did New England swing so much against Trump?

[Alben Barkley]

I said it before the election and I'll say it again now: The only reason Trump did relatively well for a Republican in New England in 2016 was that people saw him as a "different" kind of Republican that was actually more moderate, especially compared to the Jesus Freaks like Cruz. Gotta remember that New England is the least religious and most highly educated area of the country, but it does have strong Republican roots (still evident today in their RINO governors), so seeing a Republican who (while clearly far from socially liberal in other respects, notably immigration) was not outwardly pious and zealous about evangelical Christianity may have been appealing to some people there. When it turned out he would be far worse in this regard than they expected (foolishly, given his open pandering to GOP social conservatism, including the selection of Pence as his running mate), they were naturally turned off and once again voted Democratic.

Reminder that religion is the single biggest predictor of how people vote, which is why even a region as white, rural, and wealthy as New England now votes Democratic. Maybe some thought Trump -- obviously not religious himself, and a Yankee (if not a New Englander) -- would be more aligned with their interests than the GOP has been in the past few decades. But again, obviously that turned out to not be the case.

[Alben Barkley]

Really high concentration of college grads vs. nationwide.  That's the bottom line.  New England being relatively secular could be a small part of the story, but with Trump improving in places like Las Vegas, L.A. and South Florida, I think it's very overrated.  

The common thread between all those places is they have a very large number of Hispanics; New England does not. That was a whole separate issue, and it has nothing to do with the fact that secularism is the most likely reason New England so sharply shifted away from Trump (even relative to trends we saw in other educated white areas), or the proven fact that religion is the single most reliable demographic predictor of how people vote. More than race, even. Unlike the Hispanics in the areas you mentioned, New Englanders are largely not just "secular;" they are actively irreligious, while most Hispanics are at least culturally Catholic even if they do not practice it devoutly. And being irreligious is the single strongest predictor of voting Democratic.