process. former president ronald reagan would turn 100 next month. as his family prepares to mark the milestone there are new disclosures about his battle with alzheimer's. >> so help me god. >> reporter: ronald reagan was the oldest president ever, 69 when he took office. he was diagnosed with alzheimer's disease five years after leaving the white house, but in a new book,s son ron reagan writes as early as three year into his first term i was feeling the first shivers of concern that something beyond mellowing was affecting his farther. he was alarmed by the first campaign debate against mondale. >> the system is still where it was with regard to -- um -- the -- with regard to the progressivity as i said. >> my heart sank as he floundered through responses, fumbling with his notes, lost for words. he looked tired and bewildered.