Well known as a revolutionary hero due to the role he played in the Revolution as well as the Civil War, had also been Lenin's right man
Trotsky was not popular within the Communist Party
Many communists remembered that between 1903 and 1917 Trotsky had opposed Lenin
Trotsky had joined the Bolsheviks in mid-1917 and many Bolsheviks believed he joined the Party to gain power rather than because he was a true Leninist
There was a lot of evidence that Zinoviev was right and Trotsky was not a true Leninist and therefore did not deserve to lead the Party