Keep in mind that when people go to these pollsters, there's a likelihood that closeted Trump voters will say they're voting for Hillary because of how ridiculous this country is about "social issues"… It's easier for them to lie to someone's face and say they're voting for a corrupt scumbag rather than a rude shmuck (I don't know why, but welcome to 2016)

All the enthusiasm is on Trump's side, I'm sure Clinton supporters won't be perked up over waiting in line for hours to vote for someone under FBI investigation
Despite any early poll results, I'd still put him behind just because the system is against him