WASHINGTON (AP) — President-elect Donald Trump has promised to end birthright citizenship as soon as he gets into office to make good on campaign promises aiming to restrict immigration and redefining what it means to be American.

But any efforts to halt the policy would face steep legal hurdles.

Birthright citizenship means anyone born in the United States automatically becomes an American citizen. It's been in place for decades and applies to children born to someone in the country illegally or in the U.S. on a tourist or student visa who plans to return to their home country.

It's not the practice of every country, and Trump and his supporters have argued that the system is being abused and that there should be tougher standards for becoming an American citizen.

But others say this is a right enshrined in the 14th Amendment to the Constitution, it would be extremely difficult to overturn and even if it's possible, it's a bad idea.

Here's a look at birthright citizenship, what Trump has said about it and the prospects for ending it:

What Trump has said about birthright citizenship

During an interview Sunday on NBC's "Meet the Press" Trump said he "absolutely" planned to halt birthright citizenship once in office.

"We're going to end that because it's ridiculous," he said.

Trump and other opponents of birthright citizenship have argued that it creates an incentive for people to come to the U.S. illegally or take part in "birth tourism," in which pregnant women enter the U.S. specifically to give birth so their children can have citizenship before returning to their home countries.

"Simply crossing the border and having a child should not entitle anyone to citizenship," said Eric Ruark, director of research for NumbersUSA, which argues for reducing immigration. The organization supports changes that would require at least one parent to be a permanent legal resident or a U.S. citizen for their children to automatically get citizenship.

Others have argued that ending birthright citizenship would profoundly damage the country.

"One of our big benefits is that people born here are citizens, are not an illegal underclass. There's better assimilation and integration of immigrants and their children because of birthright citizenship," said Alex Nowrasteh, vice president for economic and social policy studies at the pro-immigration Cato Institute.

In 2019, the Migration Policy Institute estimated that 5.5 million children under age 18 lived with at least one parent in the country illegally in 2019, representing 7% of the U.S. child population. The vast majority of those children were U.S. citizens.

The nonpartisan think tank said during Trump's campaign for president in 2015 that the number of people in the country illegally would "balloon" if birthright citizenship were repealed, creating "a self-perpetuating class that would be excluded from social membership for generations."

What does the law say?

In the aftermath of the Civil War, Congress ratified the 14th Amendment in July 1868. That amendment assured citizenship for all, including Black people.

"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," the 14th Amendment says. "No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States."

But the 14th Amendment didn't always translate to everyone being afforded birthright citizenship. For example, it wasn't until 1924 that Congress finally granted citizenship to all Native Americans born in the U.S.

A key case in the history of birthright citizenship came in 1898, when the U.S. Supreme Court ruled that Wong Kim Ark, born in San Francisco to Chinese immigrants, was a U.S. citizen because he was born in the states. The federal government had tried to deny him reentry into the county after a trip abroad on grounds he wasn't a citizen under the Chinese Exclusion Act.

But some have argued that the 1898 case clearly applied to children born of parents who are both legal immigrants to America but that it's less clear whether it applies to children born to parents without legal status or, for example, who come for a short-term like a tourist visa.

"That is the leading case on this. In fact, it's the only case on this," said Andrew Arthur, a fellow at the Center for Immigration Studies, which supports immigration restrictions. "It's a lot more of an open legal question than most people think."

Some proponents of immigration restrictions have argued the words "subject to the jurisdiction thereof" in the 14th Amendment allows the U.S. to deny citizenship to babies born to those in the country illegally. Trump himself used that language in his 2023 announcement that he would aim to end birthright citizenship if reelected.

So what could Trump do and would it be successful?

Trump wasn't clear in his Sunday interview how he aims to end birthright citizenship.

Asked how he could get around the 14th Amendment with an executive action, Trump said: "Well, we're going to have to get it changed. We'll maybe have to go back to the people. But we have to end it." Pressed further on whether he'd use an executive order, Trump said "if we can, through executive action."

He gave a lot more details in a 2023 post on his campaign website. In it, he said he would issue an executive order the first day of his presidency, making it clear that federal agencies "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."

Trump wrote that the executive order would make clear that children of people in the U.S. illegally "should not be issued passports, Social Security numbers, or be eligible for certain taxpayer funded welfare benefits."

This would almost certainly end up in litigation.

Nowrasteh from the Cato Institute said the law is clear that birthright citizenship can't be ended by executive order but that Trump may be inclined to take a shot anyway through the courts.

"I don't take his statements very seriously. He has been saying things like this for almost a decade," Nowrasteh said. "He didn't do anything to further this agenda when he was president before. The law and judges are near uniformly opposed to his legal theory that the children of illegal immigrants born in the United States are not citizens."

Trump could steer Congress to pass a law to end birthright citizenship but would still face a legal challenge that it violates the Constitution.

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Associated Press reporter Elliot Spagat in San Diego contributed to this report.