ROBERT SIEGEL, HOST:

The GOP presidential race has been dealing this week with Donald Trump's ideas about immigration. And those include ending birthright citizenship - the idea that if you're born here, you're a citizen, even if your parents aren't. Trump's proposals raise several legal questions. And we're going to put them now to Suzanna Sherry, who teaches constitutional law at Vanderbilt University. Welcome to the program.

SUZANNA SHERRY: Thank you, Robert.

SIEGEL: Is the right carved in stone in the U.S. Constitution?

SHERRY: Yes. It's the very first sentence of the 14th amendment, which reads (reading) 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.

SIEGEL: Subject to the jurisdiction thereof - meaning?

SHERRY: That means that they are subject to the laws of the United States, that they can, for example, be prosecuted for violating American law. There are people who cannot be prosecuted for violating American law. For example, foreign ambassadors and their families have diplomatic immunity. And if an ambassador has a child here in the United States, that child will not be an American citizen.

SIEGEL: Describe for us the political context in the 1860s when this provision is written into the - well, the first sentence of the 14th Amendment.

SHERRY: The main thing that the first sentence was designed to do was to reverse the Dred Scott case, which had been decided in 1857 and which held that freed slaves were not citizens of a state. And so this phrase was to ensure that freed slaves would be considered citizens both of the United States and of the individual state where they lived.

There was some generalized discussion about whether birth was good enough to give citizenship. But it was very generalized in the sense that the United States had experienced quite a bit of immigration, and immigration was viewed as a very good thing. And so this was essentially putting out a welcome mat to immigrants by ensuring that their children born here would be citizens.

SIEGEL: I read about the 1898 case that the Supreme Court decided. It was about a 22-year-old San Francisco native named Wong Kim Ark, who was born in California to Chinese parents, went back to China, came back on the steamship Coptic and was intercepted. And he claimed, hey, I'm a citizen of this country; I have a right to live here. And the Supreme Court a couple years later said indeed, he's right. That seems to have been the decision that interpreted the 14th Amendment when it comes to birthright citizenship.

SHERRY: Yes. It was the first one that actually raised the issue. And the courts have been consistent in holding that anyone born here - other than, say, children of ambassadors - is a citizen of the United States.

SIEGEL: And in the case of Wong Kim Ark, it meant that he could not be kept out of the country under the Chinese Exclusion Act.

SHERRY: Exactly. So even though he could not have legally entered the country had he not been born here, he was a citizen. And it's essentially the same thing with children who are born here when their parents are not here legally. They have citizenship because they were born here.

SIEGEL: There are Americans born overseas to American parents or in some U.S. territories whose citizenship evidently is not guaranteed by the 14th Amendment. There's a statute that takes care of their situation.

SHERRY: That's correct because the Constitution doesn't define citizenship other than in the 14th Amendment. Congress had to figure out what to do about people who were born abroad of American parents. Now, the United States is quite unusual in having birthright citizenship, but most countries say no matter where in the world you're born, if your parents are citizens of this country, then you are a citizen of this country. And so it was assumed, I think, that children born abroad of American parents would be citizens, and then just Congress made it official.

SIEGEL: So when you hear this proposal being made by, in this case, Donald Trump, you assume he is proposing a constitutional amendment. If he wanted to change that aspect of citizenship, you would have to amend the 14th Amendment - no other way.

SHERRY: Well, you'd either have to amend the 14th Amendment, or you would have to convince the U.S. Supreme Court to overturn their earlier precedent and rule that the 14th Amendment only applies to people whose parents are legally here.

SIEGEL: Professor Sherry, thanks for talking with us about it today.

SHERRY: My pleasure.

SIEGEL: Suzanna Sherry is a professor of law at Vanderbilt University. Transcript provided by NPR, Copyright NPR.