In an article about Sagan’s life, his former student David Morrison writes:
Sagan was nominated for membership in the National Academy of Sciences. Academy membership requires distinguished research scholarship, but that is rarely sufficient to ensure membership. Considerable weight is also given to public service, as well as more political factors such as where a nominee works and whom he or she knows. Most colleagues agreed that Sagan’s research record was more than adequate (Shermer 1999), and that his additional journal editorship, government service, and contributions to public understanding of science should have ensured his election. But Sagan was blackballed in the first voting round, requiring a full debate and vote by the Academy membership. In the final vote he barely received 50 per cent yes votes, far short of the two-thirds majority required for election to membership.
Two years later, the National Academy awarded Sagan its prestigious Public Welfare Medal, perhaps in partial compensation for his earlier rejection. The damage was done, however: not only a stinging personal blow, but also an attack on his credibility as a spokesperson for science. For all his accomplishments — or perhaps because of some of them — influential members of the academic “old boys” network never accepted him.
It’s not entirely clear why Sagan was blackballed, but one person at the meeting claims it was because the astronomer had done so much television work. His Ivory Tower colleagues looked down on Cosmos as “fluff”. We’ll never know for sure why he was denied entrance, although Sagan himself said he wasn’t at all surprised.
(h/t Carl Zimmer)