In OTL, Stalin came to power in a 5 way struggle (Zinoviev/kamenev, Trotsky, Stalin, Bukharin, Rykov/tomsky) thanks to the numerous positions he was delegated by the other members of the politburo to keep him quiet.
But Trotsky had an Ace in the Hole. Lenin wrote a postscript in his last testament, saying Stalin had to be removed. For some strage reason, trotsky didn't read it out loud, thus ironically saving Stalin.
What if he did?