At this stage, odds probably favor Trump winning a second term.
They are just odds, and not certain, however. Biden should definitely not concede! There are lots of mail-in votes to be counted. Long odds are not zero odds.
The trouble is, even if Biden wins, America very much still loses. A Trumpism that almost wins despite a badly mismanaged pandemic is an amazingly successful and resilient platform. It is a very different thing from a Trumpism that loses resoundingly, which would have prompted a recalculation.
What was the most likely problem? I think it was the tactic of making this a referendum on Trump. The opposition in Italy tried to make elections a referendum on Berlusconi. They failed. The opposition in Venezuela tried to make elections a referendum on Chávez. They failed. I was worried about this tactic early on, then let those worries go, prompted by the siren song of negative partisanship (which always made a great deal of sense to me).
It turns out that lessons learned from bitter experience with actual campaigns against actual authoritarian populists were more relevant than academic theories.