Q: What is the main difference between succession under the tsarist regime and under socialism?
A: Under the tsarist regime, power was transferred from father to son, and under socialism – from grandfather to grandfather.
Also on point:
A man walks into a shop and asks, "You wouldn't happen to have any fish, would you?" The shop assistant replies, "You've got it wrong – ours is a dairy shop. We don't have any milk. You're looking for the fish shop across the road. There they don't have any fish!"
During the tsardom, tsars passed power like kings do.
Soviet union, the party chose its leader. There was a period in the Soviet times where each succeeding leader was pretty much as old as the outgoing one so they didn't last very long. It was called the gerontocracy.