"Obama, in the course of your day, you and your staff probably interact with many foreign diplomats and other persons which this system is likely to classify as 51% likely to be foreign. On top of that, the content of those conversation, depending on the topic at hand, is likely to include words that would trigger an alert. With this in mind, do you think it is acceptable that those in the NSA, many of whom may have a differing political affiliation than you, can read any correspondence flagged for review? Furthermore, how can any member of congress operate from a position of equality if they cannot have confidence that their communications could fall into the hands of their compatriots across the aisle that may have a different agenda?"
If the answer to those questions included a filter that excluded all members of the executive, legislative and judicial, the obvious follow up question would be, "Why are members of congress allowed this right, but not the citizens of this country?"
I would also take comments he made on the Wikileaks Manning trove and present them as counterpoints to any rebuttal he has. I don't remember anything verbatim, but I remember him specifically addressing the importance of American diplomats being able to be secure in their communications to be able to carry out the roles for which they were appointed. This exact same argument can be applied to every single elected representative of the people and every official appointed by a duly elected representative.