How do you know? How do we know he's not? The point here is that if he's not, then the Constitution is usurped, and the voters cheated. All the suit was asking was for him to provide proof of citizenship...that's it. He did not. And, the case was dismissed by the judge at the circuit court level, and is being appealed to the Supreme Court...plus there are 8 other suits in other states as well.
Being born of an American does not automatically make you a citizen. Especially when the American hasn't lived long enough in the U.S. to pass on citizenship. AND, he would be a NATURALIZED citizen, NOT a NATURAL BORN citizen.
FAIL. Join the flock.