This is a question that's plagued me for years. In Godfather II, Michael Corleone needs a gaming license from Nevada Senator Geary. Geary decides to squeeze the Corleones for the license. Michael refuses to play ball, saying he won't pay more than the license is worth and would rather pay nothing for it. So the two part ways. Some time later, Sen. Geary wakes up in a Corleone-run hotel next to a dead hooker, unable to remember the night before. The Corleones protect Geary and keep the press from finding out about the incident. In return, they get their gaming license, and Geary becomes a close friend of the family, going on Cuban junkets with Fredo and saying nice things about Italian Americans during Michael's trial.
I guess it's all a little too convenient and coincidental. But did the Corleones really set him up? Did they give him some sort of amnesia-inducing drug, slice up a prostitute, and put the body in his room? That's quite a bit to orchestrate.