My other marker is either Harris or Biden are completely fine and there's no data establishing either will guaranteed lose OR win. So the number one task of the party is to avoid the kind of nasty public fight that downed Carter, no matter what the naboobs in media say.
It is perfectly fine to have concerns about Biden's age, stamina, and electability. It is not ok to repeat rw memes about dementia. And people should be aware if Biden is perceived to have been pushed out in a palace coup, instead of stepping down of his own accord, it's not going to end well.
