How did the polls get it wrong? by The Economist.
The electoral map leaves no doubt as to how Mr Trump won. In states where white voters tend to be well-educated, such as Colorado and Virginia, the polls pegged the final results perfectly.
Conversely, in northern states that have lots of whites without a college degree, Mr Trump blew his polls away — including ones he is still expected to lose, but by a far smaller margin than expected, such as Minnesota.
The simplest explanation for this would be that these voters preferred him by an even larger margin than pollsters foresaw — the so-called “shy Trump” phenomenon, in which people might be wary of admitting they supported him. But in fact, the 29-point margin he ran up with this group was an almost perfect match for the 30-point gap that showed up in previous polling.
That suggests an alternate interpretation: this group, which historically has had a low propensity to vote, turned out in far greater numbers than pollsters could predict.
In other words, lots of people who hadn’t voted before turned out to vote for Trump — finally there was a candidate worth voting for, against the establishment.