Outside of Biden voluntarily stepping down, the other option is for Harris to begin 25th amendment procedures. That of course exposes KH to probing questions about exactly when she and other cabinet officials became aware of Biden's cognitive issues.
Questions you don't want asked when you're already less popular than the dementia addled President you are trying to replace.
Quite the messy pickle the dems have gotten themselves into with a dementia POTUS and DEI VP isn't it?