Michael, through Tom turns the tables on Geary 100% with the hooker. Tom leads him through a series of questions where it becomes clear that without Michael's help there is a damn good circumstantial case for manslaughter, against the senator and the likelihood that his career is over. In classic Corleone fashion, Tom explains the Senator has only one choice, and that is to accept Michael's "friendship," because that's literally all he has left if he wants to continue his career.
I always thought that was Tom at his most repellent. Downright reptilian.