Apples and oranges. His "stutter" which is debatable, has nothing to do with his declining cognitive skills. You know, I know, everyone knows he's falling apart and it's not your intellect which prevents you from acknowledging that, it's your political bias. It's extremely dangerous to have him in the position of president given his declining state of mind and you know it.
He has declining cognitive skills and he does have a speech impediment which he has always had, it can be seen going back all his career. The only reason he was elected when everyone wanted a younger man is the other old guy thought China had a hurricane making machine and wanted to shoot protestors 'just in the legs'. It was an emergency to save the US.
As Mark Esper showed, when there is a deficiency the executive staff make up for it in large part unless its all yes men.
Its a speech impediment, he gets a little phased out when tired but his experience and temper are still good as he listens to advice. Which democrat would you have run instead?
