Originally Posted by mustachepete
I think that Vito would have told Michael that no one could tell Sonny what was good for him.

I think that any trouble between Michael and Tom would be that they're both intellectuals. This makes Tom somewhat redundant, but it also makes him a potential critic - and Michael can't abide that.
Tom “could tell Sonny what was good for him” and Sonny did listen to Tom, among others -
1. Sonny agreed to wait until Michael's We can't wait Killing Pop is the key for Sollozzo
2. Sonny didn't go after Tattaglia

As far as I can recall, the only time we saw the “critic” Tom was when Tom tried to discourage Michael from killing Roth which was “Difficult not impossible” and was a success indeed

Tom couldn't see that Roth would always have been dangerous threat to Michael - kill or be killed

Tom and Fredo
Originally Posted by Lana
Michael was exasperated, frustrated having to spell everything out to Tom "even in what seemed routine matters, Tom was still no good" trying to get straight answers from him and informing Tom of things that Tom should have known [should be the other way around] eg: Roth seeking refuge in various countries

Tom seemed clueless "Duh-h-h, Tom!"
I believe "any trouble between Michael and Tom" was due to among others, the above

Both Vito and Michael knew Tom was not a wartime consigliere but I don't believe either blamed Tom for Sonny's death