Donald Trump has vowed to end birthright citizenship for children of illegal immigrants on his first day in office if he is elected in 2024.
The frontrunner for the Republican nomination said he would issue an executive order to stop babies of those who have entered the country unlawfully from automatically becoming US citizens.
Birthright citizenship arises from the 14th Amendment to the US Constitution which was ratified in 1868, three years after the end of the Civil War.
The amendment granted citizenship to anyone “born or naturalised in the United States”, including formerly enslaved people.
It has been interpreted to apply whether or not parents are in the country legally.
Mr Trump’s proposed order would declare that at least one parent must be a US citizen, or a lawful permanent resident, for their children to be a citizen.
In a campaign video, Mr Trump said his order would “choke off a major incentive for continued illegal immigration, deter more migrants from coming, and encourage many of the aliens Joe Biden has unlawfully let into our country to go”.
Mr Trump had indicated he would pursue the measure in his first term as president but stopped short of doing so.
It came as Ron DeSantis, Mr Trump’s main rival for the Republican nomination, stepped up his attacks when he kicked off his first campaign event in Iowa.
Mr DeSantis attacked Mr Trump on immigration, his handling of the pandemic, and government spending.
He suggested Mr Trump had drifted away from conservative principles as president.
Mr DeSantis said: “Unfortunately, he’s decided to move left on some of these issues. I think he’s doing it in a way that the voters are going to side with me.
“Hell, his whole family moved to Florida under my governorship.”
Mr DeSantis told a crowd packed inside a church in Des Moines, Iowa that the US was “going in the wrong direction”.
He added: “We can see it, and we can feel it.”
In response, a spokesman for Mr Trump said: “Ron DeSantis is not a serious person who can take on Joe Biden and bring about the Great American Comeback.”
The Florida governor was spending two days in Iowa, which will be the first state to vote, and was introduced by its Republican governor Kim Reynolds.
Mr DeSantis will move on to campaign in the other early-voting states of New Hampshire and South Carolina.
Mr Trump will also be campaigning this week in Iowa.
More nonsense from Donald Trump last night. Fact: He promised to build a big beautiful wall on the border. Fact: He did not deliver & immigrants are pouring over the border. Fact: He said Mexico would pay for it. Fact: We have not gotten one peso yet. He failed us on immigration.
— Chris Christie (@GovChristie) May 11, 2023
Meanwhile, Chris Christie, the former New Jersey governor, is expected to launch his 2024 campaign next week.
Mr Christie, a former ally of Mr Trump, has recently called him a “coward” and “Putin’s puppet”.
He has put himself forward as a candidate who, unlike others, will attack Mr Trump head-on.
In 2016, Mr Christie’s previous presidential campaign failed to gain traction amid a crowded field that included Mr Trump.
A Reuters/Ipsos poll last month showed only one per cent of Republicans said Mr Christie would be their preferred nominee in 2024.
In March, Mr Christie said he would not vote for Mr Trump in 2024 even if the former president was the Republican nominee.
Meanwhile, Mr Trump criticised his own former White House press secretary Kayleigh McEnany, accusing her of giving wrong poll numbers during an appearance on Fox News.
Mr Trump wrote on Truth Social: “Kayleigh ‘Milktoast’ McEnany just gave out the wrong poll numbers on Fox News.
“I am 34 points up on DeSanctimonious, not 25 up. While 25 is great, it’s not 34. She knew the number was corrected upwards by the group that did the poll. FoxNews should only use REAL Stars!!!”