I would say, this site’s record is quite close to the mark:
http://projects.fivethirtyeight.com/election-2016/delegate-targets/democrats/
I think it is harder for the pollsters now.
I know along with my wife one of my sons has not been polled at all this year which has never happened.
We have people form non parties and Dems voting for republicans, because the ones I know say they are fed up of the two Dems and do not represent them and so they voted for Trump.
Like the poll you posted, it is just about republicans and watching the news the other day from a diner I was told those WI voters know what they are voting for only to ask one woman less than hour before she voted she did not know yet. Asked another guy and he said the same.