 cerebellar or other central neurological disorders such as a stroke, multiple sclerosis, Parkinson's or ascending lateral sclerosis." She would not say if a Parkinson's expert who visited the White House several times ever participated in care for the president. In Friday's interview on ABC, the president said he didn't need to take a cognitive test. He's since written a letter to fellow Democrats insisting he's still running. He writes, the question of how to move forward has been well aired for over a week now and it's time for it to end.