President Donald Trump said he’s considering an executive order to remove the right to citizenship for babies born in the U.S. to parents who aren’t citizens ― a right enshrined in the 14th Amendment that could likely be changed only through a constitutional amendment.

Trump said in an interview with “Axios on HBO” taped Monday that he could execute the change via executive order.

“It was always told to me that you needed a constitutional amendment. Guess what? You don’t,” Trump said. “You can definitely do it with an act of Congress. But now they’re saying I can do it just with an executive order.”

He said the right awarded to babies born as birthright Americans is “ridiculous” and that the system “has to end.”

Trump also falsely stated that the U.S. is “the only country in the world” that offers citizenship to those born here. More than 30 nations, including Canada and Mexico, have similar policies.

It’s not clear what the executive order would look like or when it would be proposed ― if Trump follows through at all, considering his tendency for pre-election bluster and warnings he has received from fellow Republicans, including House Speaker Paul Ryan (Wis.), who have said doing so would be outside the bounds the president’s authority.

All babies born in the U.S. are American citizens under the Constitution’s 14th Amendment, which cannot be changed by presidential order.

Changing that policy would dramatically reshape the U.S. ― effectively punishing the children of undocumented immigrants, whom Trump has vowed to remove from the country. Even if he doesn’t follow through or succeed, though, Trump’s vow to try aligns with other messaging and actions attacking undocumented immigrants ahead of the midterm elections next Tuesday.

Exclusive: Trump to terminate birthright citizenship https://t.co/ckg0vs4T9O — Jonathan Swan (@jonathanvswan) October 30, 2018

An executive order challenging birthright citizenship would ensure a legal battle, in which most experts think the president would fail. The Supreme Court ruled in 1898’s U.S. v. Wong Kim Ark that a child born in the U.S. to immigrant parents was a citizen under the 14th Amendment.

“The president cannot erase the Constitution with an executive order, and the 14th Amendment’s citizenship guarantee is clear,” said Omar Jadwat, director of the ACLU’s Immigrants’ Rights Project. “This is a transparent and blatantly unconstitutional attempt to sow division and fan the flames of anti-immigrant hatred in the days ahead of the midterms.”

Some Republicans ― including Ryan ― quickly shot down Trump’s idea. “You cannot end birthright citizenship with an executive order,” the House speaker said Tuesday on WVLK Radio, according to Bloomberg News reporter Erik Wasson.

Rep. Carlos Curbelo (R-Fla.) criticized the president’s statement, calling instead for immigration reform “that makes our country more secure and reaffirms our wonderful tradition as a nation of immigrants.”

Another Republican, Rep. Justin Amash of Michigan, also tweeted that such an executive order would not be possible.

A president cannot amend Constitution or laws via executive order. Concept of natural-born citizen in #14thAmendment derives from natural-born subject in Britain. Phrase “and subject to the jurisdiction thereof” excludes mainly foreign diplomats, who are not subject to U.S. laws. — Justin Amash (@justinamash) October 30, 2018

The are some experts who disagree. Axios cited John Eastman, a constitutional law professor at Chapman University and director of The Claremont Institute’s Center for Constitutional Jurisprudence, who said the amendment has been misapplied and was not intended to apply to every person born in the U.S. regardless of parentage.

Sen. Lindsey Graham (R-S.C.) announced Tuesday that he would introduce legislation “along the same lines as the proposed executive order from President Trump” to end birthright citizenship, a policy change he has supported for years. It’s unclear what his legislation would look like ― and he has previously suggested such a change would require a constitutional amendment.

“This policy is a magnet for illegal immigration, out of the mainstream of the developed world, and needs to come to an end,” Graham said in a statement on Tuesday.

Trump has long supported ending birthright citizenship, recommending in 2015 on the campaign trail that the country “start a process” to scrap it.

“I don’t think they have American citizenship and if you speak to some very, very good lawyers — and I know some will disagree — but many of them agree with me and you’re going to find they do not have American citizenship. Our country is going to hell,” Trump said then in an interview with CNN.

Every time you see a Caravan, or people illegally coming, or attempting to come, into our Country illegally, think of and blame the Democrats for not giving us the votes to change our pathetic Immigration Laws! Remember the Midterms! So unfair to those who come in legally. — Donald J. Trump (@realDonaldTrump) October 22, 2018

The president has lasered in on immigration ahead of next week’s midterm elections, stoking fear about the caravan of migrants heading toward the U.S.-Mexico border from Central America. He has falsely claimed the caravan is stocked with criminals, gang members and Middle Eastern terrorists, and has threatened to cut off aid to Honduras, El Salvador and Guatemala, the countries where most of the migrants hail from.

He deployed 5,200 active-duty troops to the border on Monday in what officials of his administration described as a necessary national security measure.

This article has been updated with additional information about the 14th Amendment, as well as with responses to Trump’s proposal and information about Graham’s intended legislation.

CORRECTION: A previous version of this story misstated John Eastman’s title. He is the director of The Claremont Institute’s Center for Constitutional Jurisprudence and a constitutional law professor at Chapman University.