Turnout is usually the determining factor at this point... and a wild card, in this election, since there are signs that there are people who will be voting in this election who haven’t done so before. Historically, when turnout is very high, Democratic candidates do well (as older, conservative voters are the ones who are the ones who vote most frequently, while younger, liberal-skewing voters are less likely - hence, when turnout is high, that means that the younger liberals are voting).
That may not hold true this time around. Ive heard too many older first timers are saying, for example on radio interviews say they’re going Trump.