Alan Lichtman, who has correctly predicted 9 of 10 last presidents (with the one exception being Bush v Gore) has said that Trump wins if Biden's replaced. Hard to see Biden winning, myself, but I thought this was an interesting one for Lichtman to hang his hat on.
But, yeah, Biden seems like he's fucked. There was one particular bit in the debate - I forget what Biden started off talking about, but he completely lost his train of thought, and that is no exaggeration, but stammering and ending with "...uh, we beat Medicaid...", and looking totally vacant while he said it. It was shocking. I know that the chatter had been going on for a long time about Biden possibly having dementia or some such, but I really don't think even Trump's team thought it could be as bad as it was. I base that on how they'd been talking about Biden being pumped full of stimulants before going on in order to preemptively explain why he'd be surprisingly lucid. Turns out they needn't have bothered. Biden fulfilled the worst expectations of his critics and then some.
If any of you have dealt with an older relative with some form of cognitive decline, you'll probably have seen them on days where they're getting things hopelessly mixed up and mumbling incoherently. That's what Biden was doing at the debate. And those of you will also know that the symptoms are amplified by things like fatigue and illness. They have good days and bad days, and points in the day when they're usually better than other points in the day. Biden has said that he was suffering from exhaustion. Understandable for a man of his age, but I don't think it's really good enough for a president of the USA to basically be unable to work past 8PM.
Something interesting is that Trump's campaign has been *relatively* quiet on Biden's clear decline since the debate. You'd think that Trump would have been practically going around with a loud hailer, crowing about it, but that's not quite happened. I think the Trump campaign would prefer that Biden stays on, considering him easier to beat than the likes of Newsom, so they're not going to contribute as much as you'd have thought to the calls to have him step aside.