I feel like Democrats underestimated how much the how emails issue would effect Clinton. It was really stupid, but the whole idea of wrongdoing that kept looming proved to be enough to alter the election. Voters do care and it's reflected by the fact that Trump is not actually gaining support but retaining his base. This is not and never has been a persuasion election, it's a turnout election which is why the Trump campaign is so hell bent on depressing Democratic turnout by saying "it's over" months out.
It didn't.
The 1st time Trump was beating Hillary in the polls was Oct. 2015.
The public had already decided a year in advance, and the polls just yo-yo'ed due to non-responce bias during various media storms.
Big rewrite history here. To pretend that the emails scandal didn't effect Clinton is just nonsense.