Biden's inability to function as a human being has been apparent almost since the outset of his term, and has been growing steadily more apparent throughout. If his incompetence was the reason for his replacement, it would have been signaled to the public a year ago, where they can control the messaging and get in a competent pick to properly run a convincing campaign.
My take is that they were betting on removing Trump from the ticket one way or the other. With him forced out, the Republicans would get in one of their people (be it Nikki Hayley or someone else), who would beat Biden, and the pseudo two party system would reestablish it's hold.
One Mar-a-Lago raid, 30 felony convictions, and one assasination attempt later, and the Democrat side of the American mafia has run out the clock, and is being forced to make a Hail Mary.
Not sure what the issue is though, honestly. Can't they just cheat like they did last time?
one can make a case for the 2020 and 2021 Liz Cheney lead investigation , with the “Jan 6th Committee”
one can make the case for Merrick Garland being Attorney General
one can make the case for August 2022 search warrant w/ classified documents at Trump's Mar-a-Lago home by the FBI.
one can make the case for November 2022 , AG Merrick Garland appointing Jack Smith to do the investigation so it would be independent.
=====
but if the goal was to prevent Trump from running in 2024 , these 4 things together made that strategy utterly STUPID, you had a limited time window and by Nov 2022 it was already too late for Trump was going to announce after the midterms (he announced the 15th of November 2022)
And any court case (after the investigation) was going to take years, with automatic delays.
And by allowing Congress and Liz Cheney to do January 6th investigations you could not really prosecute him for that, not in a legal, but in a practical investigation matter for the Fed Justice Dept and Congress investigating would have conflicts of interest with turf, subpoenas, witness testimony, etc.
=====
So I repeat if this was their strategy, they were bad at implementing it. They had to choose and act immediately in 2021 and we were already having multiple crisies and lack of faith in the system at that time.