Don't change the subject, the conversation was about the power of Congress to determine how citizenship is conferred. Where was Congress given that power. It's relevant to citizenship if he was not born in the US, and could be relevant if he was born in the US of a non citizen father, which he admits to. Not to citizenship of course, but to "natural born citizenship".
I don't think that was what the conversation is about. That branch of the discussion only applies to people born outside the US.
For people born in the US, the 14th Ammendment specifies that they are are citizens. So if Obama was born here, what does a discussion about the powers of Congress have to do with anything?