It may not excuse the act, or do a thing to justify it in the view of the court, but it changes the intent and effect of the act from simple espionage to something closer to civil disobedience.
That doesn't mean he'll get away with it, or that the P****ng Marines will, either. Politics will have an impact on the fates of both.
Manning attracted so much support for what many consider an act of civil disobedience that he might have gotten away with a less ambitious crime – one that wasn't among the largest breaches of classified data in the history of the U.S. military or State Departments, for example.
If the P****ng Marines hadn't gone viral, on the other hand, the worst punishment they could have expected would have been a dressing down from a superior officer.
They may still not be prosecuted.
As indefensible as it is to urinate on a corpse – and as weak a reason as they had for doing it, compared to Manning's – it doesn't seem as if they really did enough damage, or did anything so clearly criminal that they should be prosecuted.
As long as they don't do something radically criminal during the investigation. Malingering, for example. Or Disrespect Toward a Superior, especially. The way these guys show disrespect, showing it to a live Superior would almost have to lead to Duelling, and even the Marines won't put up with that.
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