After Lenin’s death in 1924 the Bolsheviks (although not out rightly stated) were in need of a new leader. The power struggle occurred from 1923-1929 and eventually Stalin effectively became the leader of the USSR due to many reasons, including the weaknesses of Trotsky.
Trotsky had not been a Bolshevik initially – he converted from the Menshevik party in 1917. Therefore some of the party members doubted him as 100% trustworthy. Within the Civil War, he had created and led the ‘Red Army’ which was still very strong, and they feared that if he had the power to do so, Trotsky would use the Red Army to begin a violent coup and take over the whole country himself. On top of this, Trotsky himself hadn’t tried to build up support within the party and consequently after Lenin’s death when the party were in debate as to how the country should be run Trotsky had a difficult time trying to put forward his ideas as many supported Stalin.
In fact Trotsky had widely underestimated Stalin as a contender for the party’s leadership. He had regarded him as inferior, which may have been true if looking at intelligence, however Trotsky’s arrogance blinded him as his disregard for anyone less intelligent than himself again lost him support, whilst Stalin was gaining it throughout the judgements he put forward and the allies he was creating.
In hindsight it is clear that this self-importance was Trotsky’s major downfall at this time because not only was he disliked but it caused him to make some crucial errors of judgement. Most significantly the decision with Stalin to not publish Lenin’s final testament, in which it was proven that Lenin disliked Stalin and believed he had too much power and couldn’t be trusted. It is clear that had this been publicised at the time Stalin would have struggled enormously to become the leader with the criticism of a popular leader before hand. However it condemned Trotsky as well