Stalin was reportedly presented with a plan to kill Hitler. He turned it down, saying, “What if they replace him with somebody who’s competent?”
I heard the same thing, but the version I heard was Churchill, not Stalin.
The way I heard it, someone asked Churchill why Britain had not attempted to have Hitler killed, to which Churchill said: “Why would we do that? Hitler is one of out best assets! God help us if he should listen to his generals!.” Or something like that.