“No person except a natural born citizen … shall be eligible to the Office of President.”
—Article II, U.S. Constitution

Forget Giuliani, McCain, Romney, Obama, and Clinton. There is only one candidate that every American envisions in the White House: oneself. Which American, at least as a child, never once daydreamed of sitting behind the big desk in the Oval Office … leader of the free world … fighting evil and protecting freedom?

And I was no different. Well, slightly different. I was born and raised in London, spoke the Queen’s English, and never heard the date 1776 mentioned in school. But as an American citizen — born to an American mother and a British father — I too dreamed of being president. Sure being prime minister was cool, my friends certainly thought so, but who dreams of being Robin when you can be Batman?

A high school teacher shattered these dreams (don’t they always?) by telling me that “natural born citizen means born in America.” Sidekick it was from then on. But while living in Brussels a few years ago, an American colleague pointed out — after I told him that he was doing his children a disservice by not having them in America — that it’s unclear whether children born to American citizens overseas really can’t be president.

Children born abroad to American parents are citizens by virtue of statute. The Immigration and Naturalization Act of 1790 states that “the children of citizens of the United States that may be born beyond the sea, or outside the limits of the United States, shall be considered as natural born citizens.” This originally just applied when the father was an American citizen, but in 1934 the law was updated to include mothers.

The 14th Amendment states: “All persons born or naturalized in the United States … are citizens of the United States.” The question is whether laws passed by Congress making the children of Americans born overseas citizens at the time of their birth exempts them from the “naturalized” clause, and therefore considers them “natural born citizens.”

This question has never been tested in practice. It was almost tested in 1968, when Governor Romney of Michigan, who was born in a Mormon colony in Chihuahua, Mexico, was being touted as a possible Republican presidential candidate. Some opponents questioned his eligibility, nicknaming him “Chihuahua George.”

His candidacy never took off and the question was never tested. But the New York Times reported on June 30, 1983, that “Mr. Romney said he had several law firms study the question and that they all concluded he was a ‘natural born citizen’ because his parents were Americans.”

James Ho, a Dallas-based constitutional lawyer, told us that the “bottom line is that there is no 100% right answer of what” natural born citizen means. There are, he said, three main theories of what natural born citizen can possibly mean: born on American soil; dependent on one’s parents, or whatever Congress decides.

According to Mr. Ho, what you “might say is the predominant theory” is that natural born citizen means born on American soil. Where justices have theorized on the subject — it’s never been specifically raised — they say that it means place of birth, Mr. Ho said. In the 1898 Supreme Court case United States v. Wong Kim Ark for example, the court, quoting Justice Curtis’ dissent in Dred Scott, said that someone born abroad does not constitute a natural born citizen.

A number of legal scholars, however, say that natural born citizen is dependent on the parents. A professor at Harvard Law School, Mark Tushnet, told us that the children of citizens born abroad “probably ought to be treated as natural born citizens.” He said that “natural born” should be interpreted as having a “fairly strong connection to the territory of the United States.”

The third theory suggests that there is no specific definition of “natural born citizen,” but rather it constitutes whatever Congress decides it constitutes. A law professor at the University of California, Vikram Amar, said that this theory is the “majority opinion among jurists” and that “natural born means citizen at the moment of birth.” Under this theory, Mr. Ho said, “Congress could give citizenship to the entire planet,” and the entire planet could then run for the presidency. Similarly, Congress could restrict eligibility too.

For the moment, the question of whether an American citizen born on foreign soil can run for president remains unclear. An estimated 2 million Americans, therefore, remain in limbo. There is of course one, albeit expensive and probably highly litigious, way to find out.

Mr. Freedman is editor of the online edition of The New York Sun and blogs at www.itshinesforall.com.