"When pollsters called, they said they were voting for Hillary."

This implies that these voters actually voted for Trump. More likely, these voters were "soft-supporters". They did not make the trip to the polls because Ms. Clinton was just not worth their effort. Such voters will still say they are voting D when a pollster asks. But without the trip to the voting booth, that vote just does not count.

By electing a too faulty candidate in 2016, the D's alienated enough of their soft support. As time went on, the alienation increased. Add in a little Russian interference, a great FB campaign paid by the Rs, and the Comey Report, maybe 500,000 soft D supporters did not make the trip to the polls. Not much in terms of popular vote, but enough to give an edge to the other candidate, who was actually quite credible in the eyes of many Americans.

But I doubt it very much that many soft D supporters changed their preferred candidate between September 2016 and November 2016. Most voted the same way; only some did not vote.

Strange that such fickleness in voter intent can write history. A sign the current system is broken.