Conversation so far:
How long was Nikolai Yezhov in power before the fall from power?
Yezhov became People's Commissar for Internal Affairs and a member of the Central Committee on 26 September 1936. Yezhov was appointed People's Commissar for Water Transport on 6 April 1938.

Question: Where was he in power?
Self-contained rewrite: where was Nikolai Yezhov in power?