I do have my doubts about the credibility of "anonymous." But whether it is the observation of an actual insider or something someone made up because they think it is believable, this part should not surprise anyone:
[N]ormal people who spend any time with Donald Trump are uncomfortable by what they witness. He stumbles, slurs, gets confused, is easily irritated, and has trouble synthesizing information, not occasionally but with regularity. Those who would claim otherwise are lying to themselves or to the country.On some level everyone who pays attention knows that the President is not mentally competent. Whether it is because of dementia or for some other reason, this account by anonymous just echoes what many others have already said, and what anyone can see in some of the video footage of the President.