Harris is a great debater but also yes an awful orator/public speaker. Good enough though to wipe the floor in a debate with the wannabe dictator. Legally she is the only one who could inherit and use the DNC campaign money and fund a potential presidential campaign for herself if Biden decides to drop out of the race. Anyone else could not because the donations were given to the Biden/Harris campaign. So replacing him with any wet dream candidate comes with major obstacles which are not benign.
Having said that, I do not believe he will be replaced. The RNC also stands by their candidate who is a convicted felon by now for crying out loud, He is only three years younger than Biden and clearly is overweight. The Republicans stand in line, they are holding the line. Eyes on the prize. Leave it to democrats to fuck it up thanks to in-house fighting and being distracted. So as @Raider of the lost Ark already mentioned, the choice is clear. Do you vote for pro democracy or fascism? And if you wish to sit this one out or even vote for orange Mussolini or a third party candidate then the US deserves what is coming to them, a fascist - or at least autocratic state. Good luck being gay, a person of color, a woman or someone who opposes the party line. But sure let's concentrate on Biden's age or a fictional fantasy candidate who will not show up in the last minute to save us. .