The greatest enemy of the left is the left. Democrats and other left-wing supporters tend to disagree with each other a lot. There's going to be a significant portion of citizens who supported Sanders but are a bit eh at Clinton. You'll notice in many of the debates Trump kept mentioning Sanders and using his words against her, trying to get Sanders supporters to vote for him.
I also feel like many of the Trump supporters are in it for the meme.
I don't know, this will be a wild one. I'm overseas so I already voted two weeks ago, but I guess we'll see soon.