Old stuff here. As time went on, it became more and more clear that @snowden was actively working against American interests via military document leaks that were completely unrelated to domestic surveillance. He betrayed an oath which is critical to maintaining national security, and it's trivially simple to ascertain that, at the least, at the time that he fled, he clearly caused damage.

Thought experiment: You're the NSA, and @snowden is in HK mid-2013 going public, and you realize he took some unknown set of highly sensitive military documents. You have to assume the worst. Just from this alone, significant damage is an obvious conclusion, just from the uncertainty of what was or was not taken. That he later said something about leaving "breadcrumbs" was either insulting or ignorant of the reality of the impact of his actions.