Bradley Manning was on a SIPRNET connected computer. Every keystroke he made, every action he took, and every file he copied was recorded by a archive drive connected to that network. At the time, if you had access to that network, it was a gentlemen's agreement that one did not go where one did not belong on that network.
Bradley Manning went into places he should not have gone and copied the information. At some point that information was passed to Wikileaks. The government knows exactly what was copied, the problem is that information that was sensitive and hasn't come out isn't in our best interest to have as public knowledge.
What damage has it done? The State Department diplomatic back channel was compromised, and that is where a lot of things happen. Foreign governments could not talk to the United States in confidence that it would not become public knowledge. That item alone has undoubtedly killed people who did not have to die. That's just one thing. It's probably enough.
Bradley Manning is simply not a good actor. He is no folk hero or iconoclast. His acts of taking and transmitting the information seems to have been nothing more than a fit of pique. He attacked female soldiers in at least one known instance prior to this. He was on his way to being removed from the Army under conditions less than honorable. This action compromised the national security of the United States for multiple reasons.
His lawyer can ask for a show of damage all he wants. The problem is Bradley Manning consented to being observed when he was given his clearance and everytime he logged into that network. He was observed by the network to have removed classified information. At least some of this information has been observed to have been released to the public. That is the government's case plain and simple.
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