After weeks of pressure to release detailed policies regarding his positions on immigration, Donald Trump published a slate of reform ideas. Among these is the call to "end birthright citizenship," whereby children born in the United States – including those of immigrant parents – automatically become American citizens. Approximately 400,000 children are born to illegal immigrants in the U.S. each year.

Trump has decried the problems of "birth tourism" and "anchor babies" – a term he defends, in which parents immigrate to the United States in order to secure American citizenship for their children. Such children qualify for a range of government benefits, and, at age 21, they can sponsor their parents for citizenship.

In March 2015, Sen. David Vitter (R-La.) sponsored an amendment to a human trafficking bill that would have changed the law regarding who qualifies for birthright citizenship: it would have required at least one immigrant parent to be a citizen, to possess a green card, or to have served in the military for the child to automatically acquire citizenship.

Now, the issue is one being put to the 2016 presidential candidates, many of whom are split over it: some favor the status quo, some oppose it, and others want it reexamined.

The question is, what does the Constitution say about birthright citizenship, and what exactly would it require to change the law?

The most relevant passage to analyze is the Citizenship Clause of the 14th Amendment, passed in 1866 and ratified in 1868, which reads:

All persons born or naturalized in the United States and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside.

Here, as always, the wording is crucial: the amendment stipulates that citizenship is granted to those who are (1) born in the United States and (2) "subject to the jurisdiction thereof." As pointed out by various scholars, including Edward J. Erler of the Claremont Institute, this language was inserted to deny citizenship to American Indians who – though living on U.S. soil – owed their allegiance to their respective self-governing tribal nations and not the U.S. government.

However, interpretations differ regarding the precise meaning of the term "subject to the jurisdiction thereof."

Those who believe that birthright citizenship can be denied to the children of non-citizen alien parents cite the original intent of the framers of the 14th Amendment.

Sen. Lyman Trumbull, chairman of the Senate Judiciary Committee during the debate over the amendment, believed that "subject to the jurisdiction thereof" meant “not owing allegiance to anybody else and being subject to the complete jurisdiction of the United States.”

George Henry Williams, a senator during the passage of the 14th Amendment and later U.S. attorney general, argued that "jurisdiction" is a more complex concept.

"Aliens," Williams wrote in 1873, "among whom are persons born here and naturalized abroad, dwelling or being in this country, are subject to the jurisdiction of the United States only to a limited extent. Political and military rights and duties do not pertain to them."

This particular conception of jurisdiction guided the majority's decision in the Supreme Court case, Elk v. Wilkins (1884). In this case, the court ruled that a Winnebago Indian, John Elk, was not a citizen – despite having renounced his tribal membership – because he did not owe the U.S. government "direct and immediate allegiance" at the time of his birth.

Since the children of Mexicans living abroad are Mexican citizens by birth, one might argue that the children of such non-citizen immigrants do not owe exclusive allegiance to the United States and thus, by the standards of these Framers, are not subject to its jurisdiction.

This narrow conception of U.S. jurisdiction could have relevance for today's argument over birthright citizenship. Indeed, in a 2011 op-ed, Sen. Vitter referred to the Elk decision to support a law that would "close the 'birthright citizenship' loophole."

Sen. Jacob Howard, perhaps the most significant and relevant framer – the author of the Citizenship Clause, wrote that the amendment does not:

...include persons born in the United States who are foreigners, aliens, who belong to the families of ambassadors or foreign ministers accredited to the Government of the United States, but will include every other class of persons. It settles the great question of citizenship and removes all doubt as to what persons are or are not citizens of the United States.

However, it is this last definition that is most damaging to the case that the children of foreign-born parents are not entitled to birthright citizenship. Howard's conception refers to a single class, the children of diplomats, not multiple categories of individuals.

This language was the basis of the Wong Kim Ark Supreme Court decision from 1898. Born in San Francisco in 1873 to Chinese parents, the Supreme Court ruled that Wong Kim Ark was a citizen by birthright. Though his parents were "subjects" of the emperor of China, they were not in the United States on behalf of the Chinese government (in the way that ambassadors and other diplomats are), and hence the court ruled that Wong Kim Ark met both criteria of the Citizenship Clause: birth on American soil and being subject to U.S. jurisdiction.

Like the opponents of automatic birthright citizenship, its defenders can also support their case by looking at the historical and legislative context of the 14th Amendment.

During the debate in Congress, Sen. Edgar Cowan of Pennsylvania worried about the consequences of extending birthright citizenship to the large numbers of Chinese immigrants on the west coast and the "Gypsies" in his home state. Cowan argued that citizenship should be preserved for “people of my own blood and lineage, people of the same religion, people of the same beliefs and traditions.”

His opponent on this issue, Sen. John Conness of California, stated that “it may be very good capital in an electioneering campaign to declaim against the Chinese" and asserted – against Cowan's warnings about the depravity of foreigners and an invasion by "the Mongol race" – that the Chinese were an “industrious people...now passing from mining into other branches of industry."

This debate shows that the members of Congress, despite disagreeing on the merits of the amendment, were aware of the implications of its wording. As James C. Ho writes, "[Senator] Howard’s colleagues vigorously debated the wisdom of his amendment – indeed, some opposed it precisely because they opposed extending birthright citizenship to the children of aliens of different races. But no Senator disputed the meaning of the amendment with respect to alien children ."

In short, there are legal arguments on both sides of the debate.

Some of the framers of the 14th Amendment did use language that states or suggests that falling under federal jurisdiction requires a direct or exclusive attachment to the United States – a concept that dates back to the country's founding, when citizenship was contingent upon an established record of multiyear residence and good moral character.

Yet when the 14th Amendment was passed and ratified, it was generally understood at the time that the wording did grant birthright citizenship to the children of non-citizen immigrants (except those born to those representing foreign powers, such as diplomats). Subsequent rulings have upheld this interpretation.

Scholars and experts also disagree as to what it would take to undo birthright citizenship. Some argue that it requires only an act by Congress (like the measure supported by Sen. Vitter), since Article I, Section 8 of the Constitution states that “the Congress shall have the power to establish a uniform rule of naturalization.” Others argue that, given the precedent of the Wong Kim Ark case and other rulings related to the 14th Amendment upholding birthright citizenship, that such a change would require a constitutional amendment.

Perhaps in 2016, 150 years after the passage of the 14th Amendment, we will re-open – and resolve – the debate on birthright citizenship.

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