As long as whatever is ailing him does not affect his mind or judgement the man should be allowed to execute his policies. Only if he lacks the courage to continue, and expresses such himself, should it be considered to replace him.
For crying out loud, the man's job is 'brain-work', not manual. All he has to do is give instruction, or summon anyone to appear before him with progress report on issues and it's done. Can he still read, can he comprehend, can he appraise issues reasonably ? So, what's the problem ? It's his head we need to be intact. If we have it, we have our president. Though desirable, Mr President does not have to be as strong as Hercules to do his job !
I see what is happening seems to be that the man is out-living the time allotted him by the political book-makers.
It's only God who can say when a man would die. So, except some people want to commit murder they should leave the poor man alone.
It's bad enough that with his frailty he is having to clean up the mess made by such healthy people as they think that they are ! And Christ ! why do they always bandy this rumour every time he travels for medical check-up. Is the man not entitled to visit his doctor, just because he is in office!? Would they rather he dropped dead while working without a break?