I think it shows how the presidency can change a person's mind about the tradeoffs between transparency and what's best for the country. Obama came into office promising to be more transparent than any president before him - and this was a big campaign issue - but he has slowly come to realize that transparency without context can be costly. That's not an excuse for what he did, but it explains why he is open to changing his mind in these circumstances.
I think there's a legal issue here too: Obama is defending a principle that allows the government to decide what information is harmful to national security interests... and not a court or congress. That's an executive prerogative he wants to uphold.
That said, it's hard to square his decision here with his decision to release those DoJ torture memos, which were very inflammatory. The same arguments can apply. I think the White House would put on a neuroscientist's hat and argue that visual depictions of torture are potentially more harmful than banal legal language describing the depicted practices.
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