Here is a graph of the presidential polls from this election so far. Most people choose narrow ranges for the y-axis in graphs like this, to draw attention to the shifts. I show the full 0%-100% range, to display how the whole American public has split. I also choose the stronger option for “smoothing,” so that each day’s measure is an average of several days on either side. The result is a highly stable advantage for Hillary Clinton all the way along.
It doesn’t really seem to have made that much difference what Trump has said, or what has been reported about Clinton’s emails and her Foundation, or how she has spent her $319 million in TV ads. It looks as if most people had their minds made up as soon as it was clear who the nominees would be.
The trend looked similar in 2012, except that it was always much closer that year.
I’d say that partisan identification outweighs almost everything, except that Trump is underperforming, for a GOP nominee, by a few points.