I doubt if top Democrats believe their nominee, Joe Biden, is capable of serving a full four year term as President. I doubt if they ever believed it. I think they plan to replace him with vice-presidential nominee Kamala Harris as soon as it becomes politically practical. Whoever or whatever it is that she will answer to, it won’t be the American people because she will not have earned a single vote for President.
Biden and Harris have both referred to their hoped-for administration as Harris-Biden, rather than Biden-Harris. If the Democrats orchestrated Biden’s nomination with the intention of replacing him before his term is finished, it is the most dishonest presidential campaign in the history of this country.