This is a slippery slope. Elites have always used the "we know best" mentality to exploit people. The real reason is obvious, our country is so split between left and right that this was always going to happen unless you had a super charismatic politician who people liked (Obama, Biden, or even Sanders). Clinton is not that. Moreover, she just spent an entire month doing nothing but courting rich people and running ads while the media got at her and Trump. If people think they both suck, then they'll vote with their party.
She is still comfortably ahead because of the electoral college, but I get the worries because turnout is not looking good.
remember people these polls are always a hint shaky unless when they ask simple question like who do you trust. that poll was a tell tell sign that america didnt trust hil nor trump during the primaries when everyone on all sides trusted bernie but some said they still would vote for one of those they didnt trust. go figure. lol.
now back to the polls again. understand who will actually answer/take the poll. it's older people for one, for two it's usually white males. so older white males. we already know what that is. thats trump city.
on average white women across the US will go for hillary over trump even if they dont like either.
the only problem dems have is like you said, if people dont show up. dems for the most part makeup like 70% of the voters . dont by that independent nonsense. if you check independents records. they are not independent. meaning they wont jumpsides when a candidate they like is on the other side. they vote for the same sides MOST of the time. now i hate this sides game period. i wish we had more choices personally. and i wont be voting for neither of those two horrible options. so the only thing the dems ever have to worry about is low voter turnout. if dems turn out trump will get destroyed like he never had a shot. if they dont turn out or barely turn out. she will barely win or barely lose.
there's a reason why republicans all over the US do everything in their power to make it harder and harder for people to vote. specifically minority groups. since most poor groups ride with dems due to their social talking points (because a lot of it is just talk no real action) and less OBVIOUS in your face racism that the repubs show you.