I don't think they'll even be that sneaky about it, especially if Biden keeps showing signs of mental decline or just totally falls apart during the debates. They will come right out and say, "You may be marking the ballot for Biden on November 3rd, but don't worry about Biden's mental state, you are really voting for Harris/Rice/Abrams. The important thing is we beat Trump, the name at the top of the ticket is irrelevant."
First tell tale warning of an imminent media turn on Dementia Joe came this afternoon with a column by NYTimes Maggie Habermand challenging him as “not the best choice for the Dems”. This will start the floodgates.