There will never be another speechwriter like Ted Sorensen, if only because there will never be a relationship like the one between Sorensen and John F. Kennedy. Staffs have mushroomed along with expectations that presidents will speak more or less incessantly, on all subjects, from Earth Days to birthdays. Burnout sets in earlier, and few writers stay with a politician for anything like the length of time Sorensen worked for Kennedy, from January 1953 to Nov. 22, 1963. Arguably, he has never stopped working for him.