"I always thought it would be Clemenza"

Any reason why Tom thinks Clemenza, not Tessio, was more likely to betray Micheal?

My guess is that Clemenza had been suspected of being involved with Paulie's betrayal, and that maybe he felt he would be on the outs with Michael once he took over. Tom also may have been less confident in Michael's chacs of success, because Michael's rejoinder is a real show of confidence. He says this betrayal was a "smart move," and Tessio was always smarter. In other words, Michael's plan to have everyone underestimate him was working so well he exposed the traitor in the Family about whom his faher warned him.

I think Mike gets too much credit for the Tessio betryal. hell Vito even said in plain english that the capo who approaches you is the traitor. IF Vito didn't tell him i doubt Mike would have figured it out

Perhaps it was the very reason that Tessio was smarter that made Tom think it would result in the opposite action. Tessio would see that Michael and Vito are planning something and be patient. It is true that Tessio was unhappy at the meeting, but neither was Clemenza so it was still "up in the air" at that point who the traitor was going to be.

From my recollection, Vito does not state that a capo will betray Michael. But we do have Michael recognizing, of the two capos, Tessio's superior intelligence and, from all appearances, the betrayal is a smart move. Tom stating that it would be Clemenza is probably just an exercise of directorial license to set up Michael's statement about Tessio.

Maybe another reason that Tom was an unfit wartime consiglieri

True he doesn't state a capo but its easy to figure out. Mike only talks to his two capos not soldiers as willie Cicci testified. the only other option is tom so mike knew barzini would try and get his smartest capo to turn against him

You forgot about Carlo.

Carlo wasn't apart of their mob family he was kept in the dark. Vito was talking about people mike supposedly could trust in the mob family. Mike already knew that Carlo was a traitor thats why he said he made him his right hand man so he could set him up. Carlo doesn't count since he was never a member of the crime family

You need to read the novel"

Tom: "I could have sworn it would have been Carlo ..."

Read the novel many times. i'm talking about the film

So, who was that guy sitting on the couch in Vito's office when Mike announced the move to Nevada, the capos stated their dissatisfaction, Tom was removed as consigliere, and for whom Vito was happy?

That was all a ploy. What i'm trying to say is that Mike never considerd Carlo a important part of the crime family. He was setting Carlo up so Carlo would be vulnerable when mike made his move. Mike knew Carlo set up Sonny he was just waiting until Vito died to kill him.

This is more understandable, we can see why Tom would have believed it may be Carlo because he had already betrayed the Corleones.