President Donald Trump says he has heard Democratic running mate Kamala Harris “does not qualify” to serve as U.S. vice president.
Ms Harris was born to a Jamaican father and Indian mother in Oakland, California, on October 20, 1964.
But a conservative professor of law has called into question its eligibility.
For years, Mr. Trump promoted a false “birther” theory that President Barack Obama was not born in the US.
Ms Harris, a California senator, was unveiled on Tuesday as the first woman of color to serve as a running mate on a major U.S. presidential card.
She is a replacement for Democratic White House candidate Joe Biden, who will challenge Mr. Trump, a Republican, in the November general election.
What did Trump say?
At Thursday’s press conference, Mr. Trump was asked about the argument against Mrs. Harris.
The president said: “I just heard today that she does not meet the requirements and by the way the lawyer who wrote that piece is a very highly qualified, very talented lawyer.
“I have no idea if that’s right. I would have assumed the Democrats would have checked that out before she is elected to run for vice president.
“But that’s very serious. You say that, they say she’s ineligible because she was not born in this country.”
The reporter replied that there was no question that Mrs. Harris was born in the US, simply that her parents at that time may not have been legal permanent residents.
Earlier on Thursday, a Trump campaign adviser, Jenna Ellis, posted a tweet from the head of the conservative group Judicial Watch, Tim Fitton.
In that tweet, Mr. Fitton asked whether Mrs. Harris “was not fit to be vice president under the ‘Citizenship Clause’ of the U.S. Constitution.”
He also shared a piece of advice published in Newsweek magazine by John Eastman, a law professor at Chapman University in California.
What is the argument of the law professor?
Prof Eastman cites Article II of the U.S. Constitution’s assertion that “no person other than a natural-born citizen … is eligible for the office of president.”
He also points out that the 14th Amendment to the Constitution states “all persons born … in the United States, and subject to its jurisdiction, are citizens”.
Prof Eastman’s argument depends on the idea that Mrs. Harris might not have been subject to U.S. jurisdiction if her parents, for example, were on student visas at the time of her daughter’s birth in California.
In 2010, Prof Eastman ran the Republican candidate for attorney general in California. He lost to Steve Cooley, who ran for Ms Harris in the general election.
After fierce backlash after the Newsweek op-ed, its editor-in-chief Nancy Cooper stood by the decision to publish, claiming on Thursday that Prof Eastman’s article “had nothing to do with racist birtherism”.
What do other constitutional experts say?
Another constitutional law expert told CBS News, the BBC’s American partner, that Prof Eastman’s argument about Mrs Harris’ qualification was “really stupid”.
Erwin Chemerinsky, the dean of the Berkeley Law School, wrote in an email: “Under section 1 of the 14th Amendment, anyone born in the United States is a citizen of the United States.
“The Supreme Court has held this since the 1890s. Kamala Harris was born in the United States.”
Laurence Tribe, a professor of constitutional law at Harvard University and a frequent critic of President Trump, called Prof. Eastman’s argument “garbage” and “racist birtherism redux.”
Jessica Levinson, a professor at Loyola Law School, told the Associated Press news agency: “Let’s just be honest about what it is: It’s just a racist trope we distort when we have a candidate of color whose parents are not citizens. were. “
How did Trump fire up the Obama ‘birther’ theory?
Back in 2011, Mr. Trump began judging theories that President Obama could have been born in Kenya.
Even when Mr. Obama produced a copy of his birth certificate in April of that year and revealed that he was born in Hawaii, Mr. Trump continued to prove that it was a “fraud.”
During a press conference in September 2016, Mr. Trump, then the candidate for the Republican White House, was asked about the matter.
He tried to take credit for doubts about Mr Obama’s suitability, telling reporters: “I’m done it. President Obama was born in the United States. Period.”
Mr. Trump also claimed in 2016 that his Republican rival Ted Cruz was ineligible to run for president because he was born in Canada as the mother of a U.S. citizen and a Cuban-born father.