"It is not necessary that a man should be born in this country, to be 'a natural born citizen.' It is only requisite that he should be a citizen by birth, and that is the case with all the children of citizens who have ever resided in this country, though born in a foreign country." - James Bayard, A Brief Exposition of the Constitution of the United States, 1833
Chief Justice John Marshall (who at that time had been Chief Justice of the US Supreme Court for more than 30 years, beginning in 1801, just 13 years after the Constitution was ratified) read Bayard's book and corrected him on one point: Congress, he said, didn't have to ask the States for permission to build post roads and military roads. They already had it.
Chief Justice Marshall added, "With this exception, I do not recollect a single statement in your book which is not, in my judgment, entirely just."
So according to Chief Justice John Marshall, all that is required for a person to be a "natural born citizen" is that he be a "citizen by birth."
Marshall joins the 40% of the Signers of the Constitution who said the same thing when the First Congress passed a law stating that children born abroad to US citizens were to be considered as natural born citizens (and were therefore eligible to the Presidency) in this opinion.
He joins William Rawle, who is a more authoritative figure than I even realized, more authoritative than I have even published to date, and who said in no uncertain terms that "every person born within the United States, its territories or districts, whether the parents are citizens or aliens, is a natural born citizen in the sense of the Constitution, and entitled to all the rights and privileges appertaining to that capacity."
He joins Alexander Hamilton, who told us that when we wanted to understand the meaning of terms in the Constitution, we should look to the English common law for their definitions.
He joins Supreme Court Justice Joseph Story, who told us that nothing was "better settled at the common law than the doctrine that the children even of aliens born in a country while the parents are resident there under the protection of the government and owing a temporary allegiance thereto are subjects by birth."
He joins St. George Tucker, James Madison, and so, so many more, in agreeing on what it takes to be eligible to be President. It requires that one be a citizen at or by birth.