Re: Harris, two major pitfalls.
1). The right will attack her as the "DEI president," she failed at the border, she's cringey, etc. No doubt they would attack any new candidate, but this will get exceptionally ugly very fast. Can she weather it or even strike back? She had very dysmal debate performances back during the 2020 primaries.
2). How many Dem voters are you going to permanently alienate by "anointing" her without the consent of the voters? Would be an issue with any new candidate, obviously.
Lastly, the right will absolutely pounce on this to claim that the Dem party has been gaslighting the public for the past few years, they're not trustworthy, etc. The optics are not good.
I'm really not sure what the best path forward is. But I don't see Biden bouncing back and if other states are being put in play, you need to react especially if there might be a down ballot effect.