Due to Biden's incredible debate performance, Democratic movers and shakers are doing more shaking than moving, and any movement is in the direction of "anyone but Biden." And they don't even know who to replace him with.
Then there are the actual logistics. This is where Ohio comes in. See, Ohio had a nomination deadline for a candidate to appear on the ballot, and that deadline was before the Democrat's convention where Biden would formally become the nominee. Now some are saying that if Biden drops out, the delegates would be able to vote their conscience for a replacement. Problem is, the Democrats have already held a virtual nominating convention to ordain Biden in advance of the Ohio deadline. This makes Biden the official, the legal nominee, making the convention itself a charade.
If, and it is a big if, the DNC plays by the rules, their rules, it would fall to the DNC to select Biden's replacement. How democratic is that?