Natural Born Citizen

 The question is simple. Section 1 of Article Two of the United States Constitution sets forth the eligibility requirements for serving as president of the United States, under clause 5 (emphasis added):

No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President; neither shall any Person be eligible to that Office who shall not have attained to the Age of thirty-five Years, and been fourteen Years a Resident within the United States.

What does the phrase "natural-born citizen" refer to? Only a natural-born citizen can be president or vice-president, but the Constitution does not define the term. The Supreme Court has never directly addressed the question in reference to the eligibility of a specific presidential or vice-presidential candidate. 

There are different opinions on this matter, none of which are clearly correct. The basis for questioning "natural-born citizenship" is generally founded on theory that the Founding Fathers used Emerich de Vattel's Law of Nation as a basis for the terminology they employed in the Constitution'. According to Vattel, a natural born citizen differs from naturalized citizens in that the natural born citizen fulfills two necessary conditions: 

1. Born on the soil of the country (jus soli) and 
2. Born of at least one parent who is already a citizen (jus sanguinis).

An additional argument has occasionally been used that a candidate may not possess dual citizenship. None of these questions concerning the meaning of the clause have ever been completely settled.  This is, strictly speaking, a question of law, not lineage. Posing the question is not a commentary on separate issues (e.g. the question itself is independent of the candidate's race, culture or worldview).

Below is a list of candidates whose eligibility has been questioned on the basis of the Constitution's "natural-born citizen" eligibility clause. As can be seen, this question has been around for well over a century, with no resolution in sight :

Presidential or VP Candidate	Born on US soil?	Parents capable of passing on birthright citizenship?	Questioned by
Chester A. Arthur  (1881-1886)	Canada???	US mother, Irish father	Democrat opponents, including attorney Arthur Hinman, argue he was born in Canada and thus ineligible.
Christopher Schurmann	Yes	German nationals	New York Tribune
Charles Evans Hughes	Yes	British father made him dual nationality with Britain	Breckinridge Long, one of Woodrow Wilson's campaign workers, Chicago Legal News
Franklin Delano Roosevelt	Yes	US mother,  US Father	Political opponents backed rumor he was born in Canada.
George Romney	Mexico	US mother,  US Father	Various
Barry Goldwater	Arizona territory, not yet a state	US mother,  US Father	Various
Lowell P. Weicker	France	US Father, British mother born in India	Various
Marco Rubio	Yes	Neither were naturalized citizens	Alan Keyes, New Jersey lawyer Mario Apuzzo, St. Petersburg Tmes
Bobby Jindal	Yes	Neither were  naturalized citizens	Charles Kerchner, St. Petersburg Tmes
Ted Cruz	Canada	American mother, Cuban father	CBS News, Washington Post, Mary McManamon, Widener U. Delaware Law school. Newsweek, Laurence Tribe (Harvard), Thomas Lee, (Fordham)
John McCain	??? (Canal Zone)	US mother,  US Father	Peter Williams NBC News
Barack Obama	??? Hawaii??	US Mother, but too young to impart citizenship if birth was not on US soil.	Hillary Clinton
Tammy Duckworth	Thailand	US father,  Thai mother	Joe Biden
Kamala Harris	Yes	Neither were naturalized citizens	Newsweek, John Eastman, former Dean of Chapman University, Fowler School of Law