What you need to know about birthright citizenship and the 14th Amendment

One week before the midterm elections, President Donald Trump claimed that with the stroke of his pen, he could change a longstanding interpretation of the U.S. Constitution to put new limits on immigration.

In an interview Monday, the president said he planned, by signing an executive order, to do away with birthright citizenship for children born in the U.S. to undocumented parents — a right currently guaranteed by the 14th Amendment.

The president’s newest claim adds to a growing list of contentious immigration proposals he’s made ahead of the midterms to motivate Republican voters, who rank immigration as a top issue this election cycle.

Though it’s unclear if, or when, the president will act to end birthright citizenship, one of his tweets from last week warning a caravan of Central American migrants that “our Military is waiting for you!” resulted in an order sending 5,200 troops to the southwest border.

“We’ll have to see whether he actually comes out with an executive order on this issue,” said Stephen Yale-Loehr, a law professor at Cornell University and co-author of a 21-volume treatise on U.S. immigration law.

“It’s unclear if he’s saying this just to get publicity and stir up his base or if he really intends” to sign an executive order, Yale-Loehr said.

“Somebody told him he could do it by executive order and that appeals to him, particularly one week before the midterm elections, and I think that's why he’s doing it now,” he said. “Immigration has always been a strong message for him and this is just the latest example.”

While the president’s comments to Axios on Monday left some questions unanswered, here are the basics.

What is the 14th Amendment?

The 14th Amendment, which grants citizenship to anyone born on U.S. soil, was ratified in 1868 after the Civil War so that recently-freed slaves could become citizens.

“All person 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,” the Amendment reads.

The U.S. is one of more than 30 other countries that also grant citizenship to children born within their borders — a fact in contrast to the president’s statement in his interview with Axios that the U.S. is the only country in the world with such a process.

Citizenship policies vary around the world, somewhat based on geography. Countries in Europe or Asia don’t have similar policies, but countries further west, including Canada and most South American nations, do.

According to Cornell's Yale-Loehr, this might be explained as “more of an accident of history.”

“When we were formed, we were more open — trying to get people to come here — and therefore were encouraging people to come, including liberal rules about citizenship,” he said.

What is birthright citizenship?

Birthright citizenship, or jus soli, a legal term that means “right of the soil,” is the right guaranteed by the 14th Amendment, and upheld by the Supreme Court, that says anyone born on U.S soil is automatically a citizen.

Trump’s pushback on what has long been interpreted as a constitutional right comes down to a phrase in the Amendment.

“This revolves around a dispute about some of the words,” Yale-Loehr said — specifically the phrase, “and subject to the jurisdiction thereof” in the middle of the Amendment.

“Conservatives would argue that because the parents are here illegally, they are not fully subject to the jurisdiction of the U.S.,” Yale-Loehr said.

“Others would argue that's a distinction without a difference because children have to obey traffic laws, criminal laws and all other laws, so the fact that their parents don’t have legal status does not make them outside the jurisdiction of U.S. laws, generally,” said Yale-Loehr, who disagrees with the conservative interpretation.

There are two Supreme Court cases that have dealt with this specific phrase of the 14th Amendment. In an 1898 case, United States v. Wong Kim Ark, a man born in San Francisco to Chinese parents was ruled to be a citizen. In a related case, in 1982, Plyler v. Doe, the court ruled that children who weren't legal citizens still had the right to a public education under the Constitution's Equal Protection Clause.

Neither case dealt precisely with children born in America to undocumented parents — especially considering there was no such thing as illegal immigration at the time.

But putting those two cases together, Yale-Loehr said, “You have a pretty compelling argument that children born in the U.S. to undocumented parents are indeed automatically U.S. citizens.”

Can the president change birthright citizenship unilaterally?

If Trump put forward an executive order instead of going through Congress to ratify the Constitution, he would have to argue that he’s not violating the Constitution but rather interpreting it in a way that prevents citizenship, Yale-Loehr said.

“He would say he's not violating the Constitution, he’s simply interpreting this phrase and he has the legal authority to interpret it how he wants — and that's what the court would have to decide,” Yale-Loehr said.

The court would then look at two aspects: whether the president has the authority to reinterpret the longstanding interpretation of a phrase in the Constitution, and what the scope of the phrase “subject to the jurisdiction thereof” is.

Yale-Loehr doesn’t think Trump’s executive order would stand up in the courts.

“I do not think the president has the legal authority to change longstanding Supreme Court precedent,” he said. Backing up that view is an opinion issued by the Department of Justice's Office of Legal Counsel in 1995, which is still binding, that states birthright citizenship can only be changed through a Constitutional amendment.

" ... The rule of citizenship acquired by birth within the United States is the law of the Constitution, it cannot be changed through legislation, but only by amending the Constitution," the opinion reads.

The other route is through Congress, which some Republicans have mentioned. Sen. Lindsey Graham, a top Republican, stood with the president Tuesday morning and said he planned to introduce legislation “along the same lines” as Trump’s proposed executive order.

In a Washington Post opinion piece from July, former National Security official Michael Anton wrote that Congress could fix the problem "easily."

"Congress could clarify legislatively that the children of noncitizens are not subject to the jurisdiction of the United States, and thus not citizens under the 14th Amendment. But given the open-borders enthusiasm of congressional leaders of both parties, that’s unlikely," he wrote.

"It falls, then, to Trump. An executive order could specify to federal agencies that the children of noncitizens are not citizens," said Anton.

In an interview on Tuesday afternoon, House Speaker Paul Ryan said he found it “very clear” that an executive order would not effectively change the Constitution.

There are conservative legal scholars who disagree, but more legal scholars predict a strong challenge in the courts if the president were to go forward with an executive order taking citizenship away from children born on U.S. soil to undocumented parents.

“I think you can debate whether it’s good policy rationale, but I think it's clear on the law that they do qualify for automatic U.S. citizenship,” Yale-Loehr said.

ABC News' Trish Turner, Jonathan Karl, Alexander Mallin and John Parkinson contributed reporting.