http://cdrkerchner.wordpress.com/2014/02/15/the-three-legged-stool-test-for-natural-born-citizen-of-the-united-states-to-constitutional-standards/

A “natural born Citizen” of the United States is a child born in the USA of two (2) U.S. Citizens. The parents can be Citizens by Birth or they can be Citizens by Naturalization after immigrating to the USA. But to create a “natural born Citizen” of the United States both parents must be Citizens at the time the child is born in the USA. See this legal reference book used by the founders and framers of our Constitution: Law of Nations or Principles of Natural Law, Vol.1 Chapter 19 Section 212, Emer de Vattel, 1758-1797.  The overwhelming majority (probably 85%+) of citizens in the United States are natural born Citizens. This clause was added for future presidents as a national security clause. It is from the group of natural born Citizens that our founders prescribed in the presidential eligibility clause in Clause 5, Section 1 of Article II of the U.S. Constitution that we shall choose a President and Commander in Chief of our military as a strong check against foreign influence via birth allegiances on the person in that singular and most powerful office. One needs all three citizenship legs to be a natural born Citizen and have sole allegiance and claim on you at birth to one and only one country — the United States: 1. Born in the USA. 2. Father must be a U.S. Citizen (born or naturalized). 3. Mother must be U.S. Citizen (born or naturalized). Like a three legged stool if you take away any of thesethree citizenship legs of the Article II constitutional intent and requirement to being a natural born Citizen, i.e., being born with unity of citizenship in and sole allegiance to the USA, the child is born with more than one country’s citizenship and claim of allegiance/citizenship on them at their birth and thus they are NOT a natural born Citizen of the United States.  And as in the analogy of a stool designed to stand on three legs and it is missing a leg, it falls down, likewise the person’s claim to natural born Citizenship fails if the person does not have all three citizenship legs required to be a natural born Citizen at the time of their birth. See the below Venn Diagram which logically and graphically shows how a natural born Citizen has the intersection and unity of all three Citizenship statuses at birth. Read this essay “ Of Trees and Plants” on basic logic which explains that being simply a “Citizen at Birth (CAB)” does not necessarily make oneself a “natural born Citizen (NBC)” at Birth. Natural born Citizens are overwhelmingly the largest subset of all American citizens. The location of birth being in the U.S. to a U.S. father and U.S. mother … all being U.S. Citizens at the time of birth is the only way one achieves natural born Citizenship status. Natural born Citizenship is gained by the laws of nature not by any man-made law or statute or even a constitutional amendment granting that status. Natural born Citizens need no act of man for their Citizenship was created by nature and nature’s Creator. Natural born Citizens of the United States have sole allegiance to one and only one country at birth … the United States. No foreign power or country can claim their allegiance under U.S. law or the Law of Nations. Over 85% of American citizens fit that requirement, i.e., born in the USA of two U.S. Citizen (born or naturalized) parents. Natural born citizens are the 3 Leaf Clovers of the American citizens, Not the 4 Leaf Clovers. It is from those 85% of American citizens that our founders and framers directed us via Article II, Section 1 of the U.S. Constitution that we shall choose our President and Commander-in-Chief, not a dual-citizen son of a foreign national and British Subject father who was never even an immigrant to this country, and said child being born a British subject himself via his foreign national father, as is the case with Obama’s birth status.

h/t Cdr Kerchner