I think the Dems biggest problem, as it typically is, is turnout. They solved it in Deep Blue cities with the Ballot harvesting, but that take logistics and organization and it's tough to scale to every state. If the 18-35 Dem vote isn't motivated by a sleepy creepy demented old man, a quick substitute with a Newsome telegenic type could turn out that group, and they don't vote on substance so the lack of time to campaign is a non issue. Your point about discerning Independents is probably the strongest point and the biggest weakness with a substituted candidate I would think.
Dems can’t just “turn out in the cities” and win a national election... Yes, Democrats run up the score in the urban areas, and that can work many states, but it can’t win a national election just on that. Dems have very high percentage districts 80%, 90% democrat, in the urban areas, but the dirty little secret is, they can’t win without those fairly consistent 45% districts throughout the non urban areas. If those non urban areas that traditionally go republican 55/45 suddenly are going 57/43 or 60/40 republican, Democrats have ZERO shot at winning a national election
Dems don’t have a superstar, and they know they don’t have a superstar, if they did, they would have tossed Biden aside at the start of the primary season and Joe would have never been allowed to run.
So, now they want to toss someone in at the last minute? That player would need to be a superstar among superstars to pull that off, and the dems just don’t have anyone that fits that bill and they know it. Doesn’t mean they won’t try, and the media will certainly be their willing ally trying to make someone look like they are, but they just don’t have anyone like that, not even close.
We will see how it plays out, but as I said if they were going to replace Biden with someone you would likely already see them pushing them heavy in the media to build them up... plant them in the consciousness, etc... they are running out of time.
So if they plan is to replace Biden, you should be seeing a media tour the likes of which you haven’t seen in a long time trying to sell the replacement to the American people even though they aren’t officially running... that will be the tell... so far I haven’t seen that.
We shall see.
Oh and for the record at least in polling Biden is down 20 points in most of those deep blue states and areas. NYS and CA for example, Biden is polling 20 points off of his 2020 numbers... Its hard to see how someone, anyone jumps in last minute, and recovers that fully.... especially with the economy, border and every other top 10 issue that voters care about the way they are.. Democrats as a whole, not just Biden, are losing on every single important topic to voters... a “Better” candidate” might help those numbers, but they are doubtful to overcome them.
Replacement of Biden honestly IMHO would be desperation to save the down ballot, and a concession the WH is lost.