On 20 January 2009 we ceased to be a nation under Rule of Law. The majority in Congress acts boldly in criminal insanity. An illegitimate usurper holds the Presidency.
Still, the question is interesting: if Obama is held a natural born citizen dint of mother’s citizenship, yet he is also a citizen of another nation — Kenya, Canada, Indonesia, or whatever — can he enter into treaties?
My first impression, based on laws of agency, is yes. Perhaps you can summarize JB’s argument otherwise.
Since there is no known record of Barry renouncing his British citizenship and no British legal "act" that would have removed his British citizenship (obtained AT BIRTH)...he continues to be a British citizen today and perhaps a U.S. Citizen (assuming birth in HI...yet to be proven).
So, at this point, "best case" scenario for him is he is a dual citizen (British & U.S.). Thus the question, of weather or not International Law (& U.S. Law) recognizes a dual citizen's ability to enter into certain (all?) treaties.