Very insightful post, Evita. I agree with what you said. Especially how Fredo was underestimated. He was such an ineffectual dunce in GF that his betrayal of Michael in II had strong impact--we probably never would have guessed he had it in him...and what else he might have tried if Michael had given him a pass. Guilt and gratitude are the most fleeting of emotions.

In addition to Tom saying that "He [Fredo] says he knows nothing, and I believe him" when in fact Fredo knew that Quesdadt belonged to Roth: Tom didn't know that Pentangeli had survived and was being held by the FBI as a witness against Michael. Tom says: "Our people with the New York detectives say he was half dead, scared, talking out loud about how you betrayed him." If "our people" knew about Pentangeli, why didn't Tom know about him? Duh-h-h, Tom!

I also agree with Oli that Michael blamed Tom for Sonny's death. He says as much in the novel after learning about Sonny's death: "He knew now that he was no wartime consigliere. Old Genco would have smelled a rat."

Back to my original question: I don't believe Michael would have told Tom about his plan to have Fredo killed because it was between Michael and Neri. Telling Tom would have made him a potential witness against Michael at a time when Michael suspected Tom might leave the family. And, Tom had spent enough time around Michael to know that he'd never give Fredo a pass. Trying to intervene would have been futile, and would have worsened his relationship with Michael.