Yes, but if I think it's a chasm, it's harder to do all of the next steps. Who wants to donate to a losing campaign? Who wants to help at the losing campaign level? So I choose NOT to head that direction....

I can't help but be reminded of this cartoon when reading that:

smbc-comics.com: Saturday Morning Breakfast Cereal

There's something to be said for that. You (personally) can't change whether Joe Biden has mental acuity problems that will ultimately doom his campaign, and you want him to win in the event that he doesn't have mental acuity problems, so you might choose to ignore the possibility that he is in a losing campaign. There's lots of precedent for that (looking at all those folks "unskewing" the polls, back in the day).

But then again, there's a downside to choosing to believe in something that might not be true. The Presidential race doesn't take place in a vacuum. There's lots of very important downballot races, and they get affected by the topline race. If Biden can't do the job of being a Presidential candidate (which is a somewhat different job than being the President), then Democrats should take that into account in how they allocate their time and dollars and their internal "voice" over party strategy.

And as you point out, no one wants to get behind a losing campaign - which also informs the discussion of whether Biden ought to step aside for someone who's got a better chance of winning. Note: whether he ought to or not, I don't think he will, because I think he believes he's got the best chance of beating Trump than any alternative scenario.