WASHINGTON —  President-elect Donald Trump has promised to end the right to citizenship for babies born in the U.S. to undocumented parents shortly after he takes office next month.

In an interview earlier this month with NBC’s “Meet the Press,” Trump said he would attempt to do so through executive action.

“Yes, we’re going to end that, because it’s ridiculous,” Trump said.

But getting rid of birthright citizenship, a principle that can be traced in the U.S. to the end of slavery and the 14th Amendment of 1868, is highly unlikely. Here’s why:

What is birthright citizenship?

There are two types of citizenship recognized by the U.S. government: one based on descent, and another based on birthplace.

The first type grants U.S. citizenship to children born abroad to at least one U.S. citizen parent. The other guarantees that right to anyone born on U.S. soil, except the children of foreign diplomats.

The 14th Amendment grants citizenship to anyone born in the U.S. It states: “All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States.”

Thirty years after its ratification, the Supreme Court ruled that birthright citizenship applied to those born in the U.S. to immigrant parents. It has been interpreted to apply regardless of a parent’s legal status.

The case centered on Wong Kim Ark, who was born in San Francisco in 1873 to Chinese parents who were lawful permanent residents. He left the U.S. temporarily at age 21 to visit his parents, who had by then moved back to China. But upon his return, he was denied entry under the Chinese Exclusion Act on the ground that he was not a citizen. The nation’s highest court ruled that the 14th Amendment made Wong a citizen.

How does the U.S. compare to the rest of the world?

During the NBC interview, Trump erroneously said the U.S. is “the only country that has it.” In fact, more than 30 countries recognize birthright citizenship, most of them in the Western Hemisphere. Most countries around the world recognize citizenship by descent.

Sam Erman, a law professor at the University of Michigan who studies citizenship, said that the U.S. modeling birthright citizenship is part of the reason more countries have it now.

“If you have it based on descent, then you can end up with people who spend their whole lives in your country and don’t get to be members — and their children, and their children’s children,” Erman said.

Birthright citizenship, he said, “works as a way to ensure that the people being governed in a place are actually part of the place.”

Could Trump end it?

In a post last year on his campaign website, Trump wrote that he would issue an executive order his first day as president, directing federal agencies to “require that at least one parent be a U.S. citizen or lawful permanent resident for their future children to become automatic U.S. citizens.”

He said the order would clarify that children of undocumented immigrants “should not be issued passports, Social Security numbers, or be eligible for certain taxpayer funded welfare benefits.”

On NBC, Trump said he would end birthright citizenship “if we can” through executive action.

Legal scholars broadly agree it is not within the president’s executive power to end birthright citizenship, leaving the courts or a constitutional amendment as the only ways to achieve a change.

Amending the Constitution is a rigorous process with a high bar that would require the approval of two-thirds of both chambers of Congress and ratification by three-fourths of each state legislature or state convention.

Targeting “anchor babies” and “birth tourism,” Trump planned to sign an executive order that would end birthright citizenship for the children of immigrants during his first term. But he skirted the issue by instead issuing a rule to deny pregnant women visas if they appeared to be coming to the U.S. primarily to give birth.

Republicans have also introduced bills in Congress to end birthright citizenship, though none have passed. In September, Sen. Lindsey Graham (R-S.C.) introduced the Birthright Citizenship Act of 2024, which would end birthright citizenship for the children of undocumented immigrants and tourists.

After Trump’s recent comments, Graham said he is also working on a constitutional amendment to end the practice, which he has vocally opposed for decades.

“One of the most valuable commodities in the world is American citizenship,” Graham said during a news conference introducing his bill. “I can understand why almost everybody in the world would want to come to America and be a citizen. But we’ve got to have an orderly process when it comes to granting American citizenship. We have to have a process that is not exploited.”

Graham has said the Supreme Court probably would take up the case, noting that there has never been a ruling by the high court involving cases of birthright citizenship in which the parents are undocumented or are on temporary visas.

But Erman, the Michigan law professor, said it’s unlikely that even the conservative-leaning court would move to end birthright citizenship.

“Wong Kim Ark was decided by a court that was quite anti-minority and quite conservative, and even there the text and the history is just really clear,” he said. “If Wong Kim Ark could win in 1898, it feels like the precedent should be able to hold in 2024.”

What opposition would Trump face?

Any move to end birthright citizenship is sure to face legal challenges.

“Citizenship is both a bundle of rights and a form of belonging. Saying these people who are citizens are not really Americans I think does a lot of damage,” Erman said.

Migration experts have warned that repealing birthright citizenship would cause the number of people in the U.S. illegally to skyrocket. Democratic lawmakers have voiced their opposition after Trump’s recent comments.

“That concept of birthright citizenship is sort of like the backbone of America. It is very much a part of the history of our nation and it should continue as such,” Rep. Adriano Espaillat (D-N.Y.) said on CNN.

Even some Republicans have disagreed with Trump. Then-House Speaker Paul Ryan broke with Trump in 2018 when he said the president could not end birthright citizenship by executive order.

“As a conservative, I’m a believer in following the plain text of the Constitution, and I think in this case the 14th Amendment is pretty clear, and that would involve a very, very lengthy constitutional process,” he said. “But where we obviously totally agree with the president is getting at the root issue here, which is unchecked illegal immigration.”