Is it possible for Leon Trotsky, anytime from Lenin's death in 1924 to his exile in 1929, to launch a "18 Brumaire-esque" coup that topples the increasingly pro-Stalin Party leadership? I know its pretty unlikely but he could use his connections to the Red Army and the support of fellow opposition Party members like Zinoviev and Kamenev to pull it off. He doesn't declare himself First Consul afterwards of course, he just repromotes himself to a higher position of power and refill the Party ranks with his supporters.