It's obviously gonna be Harris. She's just in a precarious political position of also being VP. Meaning she can't really speak out loud that the boss is unfit to lead (she would also have to explain why the 25th hasn't been invoked yet).

So she just has to put her name quietly on the ticket and present herself as 100% in line with Joe so that the Dems have an excuse to replace same with same, but younger.