The thing the libs/"moderates"/"centrists" don't seem to understand is that this vote has long been stollen from leftists by the DNC when they decided not to run a Democratic Primary.
So for lefties it's a "choose between Charles Mason and Jack The Ripper" vote: a false choice.
The only real choice for lefties in this vote is explained by Game Theory:
Basically what you have here is a situation with entity A and entity B, that happens in rounds. Entity A chooses how to share something between A and B get, entity B decides to "accept" - in which case they both get their shares as decided by A - or "reject" in which case none of them gets anything.
In simplified terms, Entity A is the DNC, Entity B are lefties, including those in the Democrat Party, rounds are the elections and what's being approprotioned is how much a presidential candidate represents each side.
What Game Theory tells us in this case, actually backed by scientific experiments carried out with actual humans, is that if Entity A divides things in a very selfish way and Entity B "accepts" rather than choose "reject", i.e. does not punish Entity A for it even at the cost of a small loss for itself, then in the next round Entity A will divide things in a just as bad or worse way for B.
It never happens that Entity A, being one that divides the cake in a very selfish way, becomes less selfish in that division after a round were Entity B chose to "accept" that division. The best you can merelly hope for as Entity B if you keep on "accepting" is that Entity A doesn't become even more selfish in the next round.
Applied to this very specific situation it means that as long as the lefties keep on accepting the choices of the DNC (who are liberals, backed by campaign contributions from very wealthy people) for who the Democrat Presidential Candidate represents the most, then for each subsequent election the choices of the DNC will be worse and worse for the lefties.
If you look at the rounds of this "game" so far - each round being an election - this is exactly what has been happenning: the only time the Democrat candidate is ever a little leftwards from the previous one is after after their votes from the left fall, which is generally when the Democrat Party loses an election.
So the correct choice for anybody on the left who wants a chance to elect a President that is more representative of their views, and that only in a future election (as the present is already lost since the DNC has already made its choice), is to "punish" by not voting (or, even better, voting a third party candidate if they find a suitable one), which does mean the DNC loses its big bet on a guy that pretty much only represents Liberals and even Zionists, even if leftis too will lose whatever tiny bit of "representation" they would get with the not-quite-as-extreme-right presidential candidate chosen by the DNC.
Do not "punish" and instead "accept" (by voting Biden) and the next round of the game (i.e. the next election) will be the same or worse.