Two other factors he had working against him were that he did not always follow the Doctrine, and was not as ruthless as he needed to be.
Zinoviev, whilst having many good points, also had a lot of points that worked against him. His positive aspects were that he had been a Bolshevik since 1903, and had worked closely with Lenin, and therefore knew the in's and out's of the party, and knew which route Lenin wanted to follow. Lenin showed his trust Zinoviev in October after he had made a mistake, by showing his forgiveness. He was made party secretary in Leningrad, thus allowing him to build a strong power base. Politically speaking he was well placed to replace Lenin because in 1919 he was made chairman of the cominturn, and became a full member of the Politburo in 1921. Finally, he was very passionate about speaking, making him an excellent orator. Zinoviev's negative points included being disliked by the public, and also by people within the party, meaning he had little support. Also, he was thought to be incompetent and vain, and regardless of his eagerness to occupy the throne, was disorganised and shabby.
Trotsky is seen by many as having been Stalin's greatest rival to be Lenin's descendant, and was seen to be his "natural successor-. He was a talented orator and intellect, and organised the military forces of the party. He had a good relationship with the Russian people, which was boosted by him leading them out of the July days. This also proved that he was a good strategist. The foremost point is that he was always seen as being Lenin's right-hand man. It is popular opinion that the prominent reason of Trotsky not replacing Lenin was due to his lack of ruthlessness. There were many chances he had to over-power Stalin, for example by attending Lenin's funeral and organising it. Instead this was handed over to Stalin, making him appear to be more supportive of Lenin and the party.