According to Ann Coulter in Slander, DS was not an aide to Nixon, but rather a low level member of the office pool in the White House Press Office. Coulter points that out because in trying to prove that the major media is not biased to the left, the left often tries to paint DS as a Republican merely because she worked in the Nixon White House. Coulter counters that political affiliation was not a criteria for Sawyer's low level position, and despite the fact that she worked in the Nixon Administration, she was and remains left of center.
http://abcnews.go.com/sections/GMA/GoodMorningAmerica/GMA_diane_sawyer_bio.html
Prior to joining CBS News, Sawyer held several positions in the Nixon administration. She was part of the Nixon-Ford transition team from 1974 to 1975. She also assisted former President Nixon in the writing of his memoirs in 1974 and 1975.