>Sulla already existed, the idea that "tradition" will keep us safe from ambition has been disproved.
There isn't anything else besides tradition. Government in all of its forms ultimate exists and runs in a manner compatible with the consent of the people. Documents, laws, institutions, policy, what have you... they all derive out of that consent, that tradition, that mythology. You have to maintain the mythology as it grows and transforms over time. Tradition can't rule with a dead hand, it is alive with each citizen, each generation. Nothing is forever.
>What kind of organization is immune to an intelligence agency?
Nothing is perfect. Intelligence agencies aren't all-powerful, and the legislators, judges, executives, and population aren't hopeless. An independent judiciary, senators with long election cycles, and a population with freedom of the press are all resistant to the influence an intelligence agency has.
>Again, we have conclusive proof that this failed with the Nixon plumbers.
Did it? Nixon was forced out of office, he didn't win. Checks and balances aren't about preventing misbehavior, they're about fixing it when it happens. How it worked with Nixon was, as far as I can determine, satisfactory.