The status of Obama's dual citizenship at the time of his birth is completely irrelevant as to his natural born citizenship status.
What is relevant is the fact that he was born in the United States.
Obama was born in the allegiance of the United States. "“All persons born in the allegiance of the king are natural born subjects, and all persons born in the allegiance of the United States are natural born citizens. Birth and allegiance go together. Such is the rule of the common law, and it is the common law of this country, as well as of England. United States v. Rhodes, 27 F Cas 785,818 (1866)
Courts on numerous times have held that a native born citizen is a citizen who is not naturalized. United States v. Schwimmer, 279 US 644, 649 (1929)(“Except for eligibility to the Presidency, naturalized citizens stand on the same footing as do native born citizens.”)
In fact, the courts on numerous occasions observed that native born citizens are natural born citizens and thus are eligible to the Presidency. Luria v. United States, 231 US 9, 22 (1913)("Under our Constitution, a naturalized citizen stands on an equal footing with the native citizen in all respects, save that of eligibility to the Presidency.")
Furthermore, if Obama was not a natural born citizen then he is either a naturalized citizen or an alien. But this is a false dilemma fallacy since Naturalization Acts do not confer citizenship on native born citizens in the United States nor is he an alien since courts have held that children born in the United States to alien parents are natural born citizen.
In Podea v. Marshall, 83 F. Supp. 216, 219-220(ED NY 1949 )
the court noted:
"It is a long recognized and well established principle that plaintiff acquired American citizenship upon his birth on September 21, 1912, at Youngstown, Ohio, even though his parents were immigrant aliens.(internal citations omitted) And it is equally well established in our law that the plaintiff, while an infant could not divest himself of such citizenship, whether by his own acts, or the acts of his parents.(internal citations omitted)
In the New Jersey Supreme Court case Benny v. O'Brien, 32 Atl 696 (1895), Justice Van Syckel addressed the issue before the court: "The question presented is whether a person born in this country of alien parents, who, prior to his birth, had their domicile here, is a citizen of the United States?"
In answering in the affirmative Justice Van Syckel declared:“The words of the fourteenth amendment are, "born in the United States and subject to the Jurisdiction thereof." Those provisions by implication concede that there may be instances in which the right to citizenship does not attach by reason of birth in this country. Two facts must concur: the person must be born here, and he must be subject to the Jurisdiction of the United States according to the fourteenth amendment, which means, according to the civil rights act, that the person born here is not subject to any foreign power. Allan Benny, whose parents were 'domiciled here at the time of his birth, is subject to the jurisdiction of the United States, and is not subject to any foreign power.” Id
As such, Obama's dual citizenship status at birth is legally irrelevant and immaterial since courts have held that mere birth in the United States is sufficient to confer natural born citizenship status.
Obama was born under the allegiance of his father's nation, which made him a citizen of that nation, he must be naturalized to be come a citizen of the US.
Of course the Constitution does not recognize a dual-citizenship status. If it does please reference.