Biden got saved by Covid. That is abundantly clear right now. Pretty much everything they banked on didn't pan out. Biden was supposed to be strong in Florida. He decisively lost it. Biden was supposed to be strong in Pennyslvania, it's an extremely tight race that could go either way. He was supposed to be able to build a multicultural coalition with strong black and Hispanic support. He did worse than Hillary in the minority vote and is about to give Trump the best GOP minority turnout since 1960. He didn't win the Senate. He actually lost seats in the House which nobody saw coming. He was supposed to bring in moderate Republicans and he didn't.
Basically Covid created a situation where there was enough dissatisfaction with Trump combined with a massive increase in mail in voting (which made it more accessible) that turnout across the board increased. It increased for Trump as well. Trump currently sits at 68.3 million votes. That outpaces Hillary's final total 4 years ago. Biden actually created an environment where Trump wildly overperfomed and did better than 2016. The increased turnout across the board was just enough to even out the margins in the rust belt that really killed Hillary because the low turnout allowed Trump to sneak in just over her.
That's pretty much what the data is showing. Biden's entire strategy going in actually backfired. Basically increased turnout (that also happened for Trump due to early voting) and some older white people who got scared of the Covid response is what is going to create an extremely narrow victory (I hope).
Trump was not strong candidate to suggest that he was unbeatable or should be doing this well. The data just doesn't bare that out on any level. It didn't in 2016 and it didn't this year. The tightness is because most of the bets the Biden campaign made just didn't work out. If Biden did everything that his campaign said they were aiming for, this would have been the wave election people were expecting. No the Democrats just made two very winnable elections very difficult because they bought into alot of allusions that you could be lazy and coast off Trump's negatives. You probably could have just run a generic Democrat who can give a good speech and mimic this result if they have nothing else going for them.