This is a broad topic and I encourage people to read widely about it. Bullying tactics is pretty much uniform over the board. These are tactics learned in the school yard to break people who do not follow the status quo. The targets of bullying are usually honest because lying psychopaths are threatened. This patten has such a repeater, school yard, USA diplomatic leaks. Strator techniques. Go forth and read, learn. Develop strategies to counter bullying techniques. If you take the psychopath out of politics then you have taken the bullet out as well.
The IM conversations that Manning had with Adrian Lamo are a matter of public record. In them, Manning states many times that he thinks that there are things happening in Iraq that are wrong, and that he wants to put an end to them. This, combined with the actual evidence contained in the footage and documents pointing to widespread abuse of prisoners, imprisonment without cause, and the cover up of civilian deaths by military personnel, show that it is a valid defense here.
You cannot hide behind the word "treason" when talking about bringing to light horrible actions. Bradley Manning let the world know some evil things that were being done in war, and that should be defended. Of course people are upset with him, but he shouldn't be punished just because he brought to light things that people don't want to talk about.
Treason is not whistle blowing. He didn't do what he did in order to better the government, or the country. He leaked sensitive classified military information and placed his fellow country men and women in harm's way. Whistle blowing does not bring harm to anyone, other than a corrupt and illegal work place.
Bradley Manning is a traitor. Leaking sensitive military intelligence, as well as diplomatic messages is not blowing the whistle on deceptive practices, or on workplace violations, it's treason. It put his fellow soldiers in danger, as well as embarrassed our diplomatic corps.
A whistleblower defense would be suitable if he uncovered something like Abu Ghraib, or soldiers harming each other under consent of their superiors, but not classified documents, or even just the documents marked internal.