I don't think stepping aside is worth it, given the party infighting that would result much closer to the election, the loss of name recognition, and incumbency advantage. Democrats would be better off publicly ignoring the suggestion of stepping aside. Stop shooting yourself in the dick and call on Republicans to clean their house, call on compromised SCOTUS justices to resign or be investigated. Now is the time to push back on the fascists, not act like everything is fine and only look inwardly.
Nope, the time for that was ~4 years ago at least.
"Sorry, was it the GQP justices I should have called on to quit?"
Yup, far better to ignore a problem than to fix it. Nothing could possibly go wrong with a Presidential candidate in noticeable cognitive decline.
Plus, what if Trump goes full-dementia first, pulls down his trousers on live TV and demonstrates that he went poopy, that would be good for the Democratic party, right? Unless of course the GQP replace him with someone who still has their marbles and then the Democratic party are caught on the back-foot and still in denial / "damage limitation mode" just when the GQP has a fresh wind in its sails and claiming that the GQP is a new party now, and the public has just had a very graphic demonstration of how ugly dementia gets.
Dementia does not wait for the least damaging time and place to fuck things up. It strikes often in stressful circumstances and unfamiliar settings. But thankfully being President involves neither of those things.
The bothsides guys are going to be laughing their asses off. It's often said that the easiest way for the right wing to get in is for people not to bother turning up to vote, and why would they when both candidates are probably due another cognitive assessment. Young people will surely be queuing around the block to vote for the epitome of "hush grandpa, take your pills", there's nothing quite like the notion that both candidates could easily be dead in the next 12 months to scream, "yes, that's absolutely the person that a 20-year-old like me should vote for, this octogenarian has their finger on the pulse of what affects young people!".
But sure, denial is definitively the best policy.
By the way, I sincerely hope I'm wrong in my predictions. I think both the US and UK seriously need to (and are well placed to) destroy conservatism in its current form, but our realistic alternatives are so fucking weak right now because neither of them really want to.
I'm also not normally calling for term limits or similar bullshit. A person simply being older should not rule them out of the running, but the US is pushing things to the extreme and is seeing predictable results.