Those three issues are not mutually exclusive in any way whatsoever. It is entirely possible and probable that they are independent and concurrent issues.
Item 1. Biden is cognitively deficient. Any suggestion that he simply has a stammer is laughable. He is displaying many symptoms of dementia or similar cognitive decline. Its horrible for him and I wish him no ill whatsoever but clearly he is not in good shape and it is impacting his performance.
Item 2. I don't think there has been any obscuring of criminal wrongdoing, what we have is the lack of political will or stomach to investigate in any thorough manner. The Biden's have links to Ukraine and China which may or may not be legitimate. Biden's son Hunter has numerous indiscretions with drugs and firearms and a job role at executive level in Ukraine for fields of expertise he does not possess at a fantastic salary. All very suspicious and not thoroughly investigated.
Item 3. If item 1 is true (and it is) then it begs the question who is running the USA? Rumours of Obama's cold hand steering things in the background have been around for ages, but clearly that is just unsubstantiated rumour and just imagine the shit storm if that turned out to be true. Unconstitutional is one word that springs to mind and the means by which the situation came about (insert conspiracy theory here) would make the plot of a great movie. Maybe we have lived through it and just don't know it yet...
Do I think he's in decline? Yes. But beyond that a lot of what you're saying is just tin hat wishful thinking especially regarding item 2 because that dreaded "E" word I keep asking you about keeps raising it's head... evidence.
It would appear the latest of the MAGA republicans smoking gun whistleblowers has just been indicted for lying to Congress about what he apparently claimed was going on. The lack of credible testimony from witnesses is only outshone by the total lack of any physical evidence. All that emerged from their deep dive into Hunter thus far has been the dick pics of Hunter Biden that Marjorie Taylor Greene has an unhealthy obsession with.
As for item 3... how does a bloke who's as cognitively impaired as you reckon he is not give the game away every time he's infront of camera if he's simply a front for another Obama lead administration?
Besides, for every example of cognitive decline in Biden there's at least one matching example of it on full display with Trump (who would himself become the oldest President ever sworn in if he wins come November - a minor detail brushed under the carpet when it suits)
Swap Biden's kids for Trump's (and give them official roles in gov't which Hunter hasn't had) and Ukraine for places like Saudi Arabia and apparent actual evidence to show that clan Trump trousered billions from some rather unsavory regimes during Trump's time in office (again conveniently overlooked).
Whatever drug problem Hunter Biden had is on full current display with Donny Junior. He's clearly off his tits most the time.
Donald hung around and partied with Epstein, brags about how his fame allowed him to finger relative strangers and get away with it, has been effectively convicted of rape, had multiple affairs, been accused of having golden shower parties with hookers and is about to be in court surrounding his hush money payments to porn stars... and Biden's the supposed pervert?
When the Democrats describe a lot of what's going on as "projection" my eyes and ears are finding it difficult to argue that they aren't wrong.
Doesn't excuse Biden of anything he might have done, but when most of the evidence that's out there consistently points in one direction and there's not much else other than wishful thinking pointing the other way - why the rush to defend the established guilty party by pointing fingers at the other? it makes zero logical sense to me