Obama is not and cannot be a natural born citizen. His father under U.S.law was Kenyan, and his stepfather may have been Indonesian and adopted Barry to make him also an Indonesian citizen.
Marco Rubio’s parents were citizens of Cuba at the time of his birth in the United States, which makes him a natural born citizen of Cuba and a possible native born citizen under statutory law of the United States at birth. Marco Rubio retained the right to denonunce his native born U.S. citizenship until his age of majority, which means he was born under the sovereignty and allegiance of Cuba and retained divided loyalty to Cuba and the United States until he lost the right of citizenship of Cuba. The authors of the Constitution wrote the natural born citizen clause for the specific purpose of making any person who was born after the adoption of the Constitution with the duty of loyalty to a foreign sovereign ineligible to occupy the office of the Commander-in-Chief of the American Army and the Office of the President. Marco Rubio was born with the duty of sovereignty to Cuba and its leadership. Being born with native born U.S. citizenship is a manmade law and not a natural law, so such native born citizenship is no better than an immigrant’s obtaining citizenship by the manmade statutory act of naturalization.
The appeals court of appeals in Ankeny v. Governor of Indiana disagrees. The constitution does not explicitly define what “natural born citizen” means. It’s been ruled that anybody with birthright citizenship is considered a natural born citizen.