That's the trouble really: he wasn't "whistle-blowing", just dumping a vast cache of the secrets he was able to get hold of. He didn't pick out actual wrongdoing, he didn't go to someone in authority - he just dumped a pile of stuff on the Internet. Even if the whole military chain of command was "compromised", there are other avenues: the Inspector General, DoD reporting lines, his Congresscritters... mad Australian rape suspects aren't exactly the first port of call for genuine whistleblowing. Indeed, most of the secret documents he published weren't even military, let alone related to his own chain of command - at most, they were sometimes embarrassing to the US and its allies.