If 0bama Sr. and Ann Dunham were married, I think there may be some chance for challenging his eligibility on the ground that the father was not a US citizen. If they were not married, it’s more likely that he had to follow the mother’s. Am I wrong?
had to follow the mother’s what?
I think you are probably right. Although this is a matter of a bit of obscurity due to the changing laws on the subject, the British law that made Obama a British colonial subject at birth may not have operated to that effect if he had been born out of wedlock to his British father.
I think the evidence is that Obama's parents WERE married (otherwise a divorce would not have been needed) and that Obama WAS a British subject at birth, and that he was not, therefore, a natural born citizen of the United States. I believe that this is the classic example is who the Framers intended to bar from the Presidency by their use of the phrase: someone who could be claimed as a national by Great Britain.
I would think that the father's name on the long form birth certificate would establish parentage, married or not. The Certificate of Live Birth form, in '61, did not even contain a field to indicate if the parents were married. It also asks for the mother's maiden name, not her married name, if any.
Thus, if the test for NBC is having two US citizen parents, he fails, IF the long Form BC shows BHO Sr as his father.
IMHO, the search for British citizenship for Junior is misplaced. It doesn't matter. Citizenship of his father, the legal one, does. If the father was not a US Citizen, the child is not an NBC. Now there are potential circumstances that would make BHO Jr. not even a citizen, unless later naturalized, but confirming those could prove difficult.