...it would depend on the situation. If he's ahead such that the mail-in vote is irrelevant (and I think that varies by state), then I'd be fine with it. As for what I mean by the mail-in vote being irrelevant, here are two scenarios:

1) One or several states' winners can't be determined yet due to uncounted mail-in ballots, but Trump doesn't need those states to win. In other words, even if he ultimately lost all of them, he'd still win the Presidency because of all the other states he clearly had already won.

2) While there are still uncounted mail-in ballots in a particular state, there's no reasonable expectation that the counting of those ballots would lead to a Biden victory in that state.

My understanding is that the vast majority of mail-in ballots will be counted on Election Day, which is good news. Basically, the only ones that would not be counted by then would be those that had not yet arrived.

That is a can of worms that, to me, just shows the idiocy of mass mail-in balloting to begin with, but that's the situation we're in unfortunately. Not sure how that would play out -- my guess is it would be Florida 2000, but possibly in multiple states with both parties contesting votes for multiple reasons. It will be all-out partisan warfare, including by Trump.

Also, I don't view this as a Trump-only concern. The same problem exists if Biden appears to have won and/or if no one appears to have won.