I've often thought that Sol would have first approached Barzini first with his deal. Sol would have figured that Vito was already on top, with businesses that were a lot safer than drugs. But Barzini--younger than the other Dons, chafing to be Numero Uno, would have had the most to gain in a deal with Sol. Barzini would have told Sol that he still needed Vito's money and influence. "Go to Tattaglia--he's a pimp, Vito's worried about him. Tell Tatt anything, but I'll be your silent partner." If Vito said yes, Barzini would get silently rich on Vito's money and influence--and Vito wouldn't even know he was making his arch-rival richer and more powerful.
Sollozzo told Michael "What happened [attempts on Vito's Life] was unavoidable
I had the unspoken support of the other Family Dons"
Whilst when Barzini actually came on board is open to debate -- my take, same as Turnbull's that Barzini was in, from day one
Also, I doubt Vito's murder would have been attempted unless sanctioned by Barzini, second in the pecking order though not a smart move! -- Killing the goose that they
needed to lay them, the golden egg
Sollozzo: I need, Don Corleone, those politicians that you carry in your pocket, like so many nickels and dimes
Sollozzo: And don't lose that famous temper of yours, huh Sonny?
If they can't talk business with hothead Sonny, how do they think? those politicians can? or Sonny himself can with those politicians?
No nickels and dimes in Sonny's pocket!
