If natural born status means one’s parents (or father) is an American at the time of the child’s birth, I’m sure there would be some rebuttable presumptions accorded the candidate.
IOW, if nothing on its face raised a question about his natural born (citizenship by descent) status, the challenger would have to come up with more than speculation to rebut the presumption that the NBS attains. And, really, that is how it should be. This is not a matter that should be challengeable by every crackpot theory out there with no evidence whatsoever.
So, you questioned if DNA evidence would be required. I would answer “not usually, probably never.” But, hey, if a president-select needed to prove his natural born (citizenship by descent) status, it would be up to him what evidence he wanted to proffer if someone actually rebutted the presumption, based on say official documents, that his father was a citizen.
In McCain’s case, for example, there is no question at all about the citizenship of his parents. It would take some piece of incredibly solid evidence to rebut the presumption that his father was an American, based on his father’s Navy records, security clearances and so on. Yet McCain’s NB status may actually still be unsettled because the SCOTUS has never quite said that natural born status is based on descent alone.
In Obama’s case, there is no doubt that his named father was not and never became an American, or that his named father passed British citizenship to Obama by descent.
If the SCOTUS came out and said the natural born status is citizenship by descent from the father, regardless of birthplace, the only thing Obama could do is claim that he now knows that his father actually was someone else who was an American. And he’d have to offer whatever evidence he thought he needed to prove that claim.
P.S. I wonder how old Obama’s father was at the time of his conception. I mean, was this even legal in Hawaii at that time.
BHO Sr was born in 36, so was about 24-25 when Jr was born. (I don’t know if it was statutory, if that’s what you are asking)