IMO the senility of either candidate is beside the point because they both have teams that will keep things running when they can’t. Hell, those teams keep things running even when the president can because it’s not a job one person can do alone.

The difference is Trump’s team is openly planning fascism while Biden’s team has to at least pretend to be opposed to that or risk more people accepting that neither party wants to oppose the ruler class.

The only time a president being lucid matters is when the president disagrees with their team, that disagreement matters for the people, and the president is on the good side of the disagreement.

And in this case, I can’t see any disagreement a lucid Trump has with his team having a good option for the prime or any disagreement a lucid Biden has with his team having a worse outcome than Trump’s team gaining power.