As it stands today, the Biden Campaign would appear quite likely but not guaranteed to win come November 3rd (or at some point thereafter). It could end early on November 3rd (if Florida appears to be trending toward Biden). Namely, it is hard to craft a scenario whereby Trump loses Florida and wins the White House. 538 has created an interactive where you can explore the inferential dynamics between the states (we learn about the likelihood in State B from the earlier results in State A). The interactive also highlights how results in early reporting states can reduce the remaining plausible paths to victory (there are only a few paths for Trump at this point).
Of course, it should be stated that remaining events or other issues could (potentially) change the dynamics or undermine the ability to leverage polls to make a proper inference. Here are few possibilities —
(1) Another October Surprise could drop between now and Election Day (there have already been several). However, it should be noted that one implication of all of this early voting is that the impact of a late October surprise is diminished.
(2) There could be systematic bias in polling (such as an unwillingness on behalf of voters to admit to pollsters their support for Trump). Alternatively, there could be a fundamental misunderstanding of the composition of the 2020 Electorate. As has been recently noted, the Trump Campaign has spent a significant amount of time on voter registration in several key battleground states. Will these newly registered folks actually vote ?
(3) Turnout dynamics associated with the cocktail of early voting, large scale absentee ballots or fear of turning up to the polls due to our latest COVID surge. Any or all could impact the final outcome.
That said, if I had to bet I would bet on Biden to win (and give far better than even money).
We do have at least some information on the state of ongoing voting thanks to the Early Voting Tracking Project by Michael McDonald.
It is unprecedented turnout thus far. On its face this would purport to favor the Biden Campaign. However, the question remains whether this is merely a cannibalization of the normal Early In Person Voting and/or Election Day In Person Voting. In other words, how much will net turnout increase? Will it make a difference?
Taking Pennsylvania as a highly probable Tipping Point State, it will be interesting to see what percentage of mail in ballots are returned in the days to come. At the County level, there is significant variation in number of returned ballots thus far (even among those who have already requested a ballot).