The Constitution does not require that both parents be citizens in order for a person to be “natural born”.
For case law, see US vs. Wong, 1897 or so. The US confers citizenship jus soli, by virtue of place of birth, not jus sanguinis, by blood.
Once again I think you are confusing Citizen with Natural Born Citizen.
The Wong VS US case was about citizenship and if he a person was born here, were they a CITIZEN. According to other SCOTUS cases, the “natural born” consists of not being being born as a subject of a foreign power, which Obama was.
I don’t doubt Obama’s citizenship, I doubt his “natural born citizenship”.