President-elect Donald Trump said he wants to end birthright citizenship on his first day in office next month. But he’ll likely run into trouble.

Trump has suggested, without offering details, that he could enact his plan through an executive order. Birthright citizenship, which gives U.S. citizenship to anyone born on the country’s soil, is built into law through the Constitution — and any attempt to remove it would likely face immediate legal action.

In 2018, Trump told Axios that he was planning to sign an executive order that would end the constitutional right in his first term, saying, “You can definitely do it with an act of Congress. But now they’re saying I can do it just with an executive order.” Trump never took action on the issue during his first administration.

This time around, it’s one of a slew of changes he’s pledging to roll out to curb immigration, in addition to implementing mass deportations of undocumented immigrants and clamping down on illegal border crossings.

We looked into what might happen to the president-elect’s plan if he tries to take action:

What is birthright citizenship and how is it a part of the Constitution?

Birthright citizenship is guaranteed by the 14th Amendment to the Constitution, enacted in 1868. The amendment states that anyone born in the United States automatically becomes a United States citizen, regardless of their parents’ immigration status.

The language of the 14th Amendment states that “all persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States.”

Can Trump end birthright citizenship through an executive order?

Not likely.

Legal experts say that no executive order can overturn the 14th Amendment because the president doesn’t have the authority to change the Constitution.

Aaron Reichlin-Melnick, a senior fellow at the American Immigration Council, said that if Trump were to issue an executive order directing the Social Security Administration to refuse to grant an identification document to a person who can’t prove that both of their parents were U.S. citizens, it would likely be challenged by the courts and eventually struck down.

“There are virtually no well-respected lawyers or academics who agree with President-elect Trump, and there is no precedent that supports the theory,” Reichlin-Melnick said.

Trump could limit immigration by executive order, making it harder for people to come into the country and have children, but birthright citizenship is a constitutionally guaranteed right, said Adam Winkler, a law professor at UCLA.

“The whole reason it is in the Constitution is to take it out of the hands of politicians,” Winkler said.

So how do you change an amendment?

Trump could attempt to end birthright citizenship through a new constitutional amendment, but it would be nearly impossible because of the extensive support required for passage. A constitutional amendment requires two-thirds of support in both houses of the U.S. Congress, and the ratification by three-fourths of state legislatures.