I don't know but you are not completely correct here. First, he has some union endorsements and the rank and file union people do not hate him, not at all.
He is winning among white women and so the idea women hate him is misleading. In general, married women favor the GOP, and white voters favor the GOP across the board.
It is true he suffers as all Republicans do, with minorities except not so much Asians, but oddly enough, polls better than Romney with Hispanics.
He also seems to be weaker with college educated whites (not HS) but on the other hand is running fairly strong with blue collar democrats. So who knows?
I think if he ran a more disciplined campaign, he'd be winning in a landslide but that's in large part due to Hillary. if the democrats had a better candidate, it wouldn't be close. Same is true for Republicans.