Why didn't Trotsky take over the USSR after Lenin?

Life of Leon Trotsky | A Biography (1879-1940)

Leon Trotsky: Communism's True Believer

What if Trotsky returned today?

Trotsky with Hitchens and Service

The Bolsheviks : Death of Trotsky - Forgotten History

What if Trotsky Came To Power Instead Of Stalin? (Ft: Cypher the Cynical Historian)