Well, let's see what might happen, plausibly, to sway folks in the middle:
Debates, that's often a big one.
More gaffes by either candidate, that can be big
A continued decline in COVID cases and clear signs the economy is recovering, that's possible.
Continued "unrest" in various cities being handled better by one candidate or the other
Continued growth in the stock market making a lot of folks feeling wealthier and thinking the status quo is OK