Answer: Leon Trotsky failed to become leader due to Stalin's influence on the politburo (the principal policymaking committee of a communist party.) and his skill at getting rid of the opposition.
Step-by-step explanation:
The elite of the communist party distrusted Trotsky because of his Menshevik past and they didn't see him as a true Bolshevik.
Bolshevism: The communist form of government adopted in Russia following the Bolshevik revolution of 1917 (The year Trotsky joined Bolshevism)
Menshevik: A member of the moderate non-Leninist wing of the Russian Social Democratic Workers' Party, opposed to the Bolsheviks and defeated by them after the overthrow of the tsar in 1917.