As Declan McCullagh points out, the executive order "allows material to be classified only if disclosure would do 'damage to the national security and the original classification authority is able to identify or describe the damage.'" He also points out that one of Obama's first acts as president was to sign a memo that said that FOIA "should be administered with a clear presumption: In the face of doubt, openness prevails. The government should not keep information confidential merely because public officials might be embarrassed by disclosure."
The claim that this treaty cannot be disclosed for national security reasons sounds bogus, but if it's so, what's the purported damage being prevented? In the absence of a clear rationale, this treaty should be openly discussed and available to the general public.