He doesnt exist in a bubble. If people in the democratic party and beyond had concern about his mental acuity they would say so. He may well end up as the leader but he will reintroduce proper government; that is to say advisors, staff, a civil service properly functioning, policies that address the strategic issues that he clearly wants to work towards and people to enact them. A leader sets a system to do this and people to make it so, and that is what he will do. Trump has a whole tranche of posts he never even filled, the functions of govt are not there because he has a cabal of family members and enablers to blag it for him. Biden is congitively sharp enough to have an administration working for him. If he is getting on a bit, then it doesnt matter. He is intellectually light years ahead of who will be replacing, and that is the important thing. Reintroduce proper governance, a separation of powers, integrity and some progressive policy. He has ideas, and a plan, which is not indicative of senility. If he stumbles over words in expressing those ideas, who cares. A senior citizen who undertands the workings of politics and diplomacy and the sensitivities of global issues is the main thing, with a functioning staff and respect for them.