Did Hillary Clinton severely blunder in losing MI, WI, and PA?

[TML]

I do agree that Hillary made a big mistake in neglecting these states - by doing little or no campaigning in WI and MI and not focusing on working class voters in PA enough. Although most of the polls showed her with leads in these three states, this election had a greater share of undecided voters in the final days of the election than most recent elections (In fact, according to FiveThirtyEight's estimates, the share of undecided voters on Election Day 2016 exceeded 10%, which was the first time that has happened since 1996). Thus, her leads in the polls were in fact vulnerable to being wiped out by late-breaking voters, especially since the polls indicated that her vote share was less than 50%. Looking back, I think the correct strategy in these states would have been to campaign there to try to get her own vote share in the polls to ~50% or better (which would have been virtually safe from late-breaking voters for her opponent).