Prove it? Seriously, are you that obtuse? Now you're arguing that Barack Obama Sr. is not the father? Good Lord.
'he is NOT a natural born citizen, is he? "
Ah, yep, he is. There is not a single US court case that has held that to qualify as a natural-born citizen, both parents must be American citizens. It's just more blather in birtherland.
There is however, a case that holds...
"Based upon the language of Article II, Section 1, Clause 4 and the guidance provided by Wong Kim Ark, we conclude that persons born within the borders of the United States are "natural born Citizens" for Article II, Section 1 purposes, regardless of the citizenship of their parents. Just as a person "born within the British dominions [was] a natural-born British subject" at the time of the framing of the U.S. Constitution, so too were those "born in the allegiance of the United States [] natural-born citizens"emphasis added
Gee, how about that?
The interpretation of the 14A by the courts couldn't be clearer. If you can come up with a Supreme Court case, Appellate Case or state case that says otherwise, please share it with everyone, won't you?