President Donald Trump says he has heard Democratic running mate Kamala Harris “doesn’t qualify” to serve as US vice-president, amplifying a fringe legal theory critics decry as racist.
Ms Harris was born to a Jamaican father and Indian mother in Oakland, California, on 20 October 1964.
But a conservative law professor has questioned her 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 colour to serve as running mate on a main-party US presidential ticket.
At Thursday’s press conference, Mr Trump was asked about the argument against Ms Harris.
The president said: “I just heard it today that she doesn’t meet the requirements and by the way the lawyer that 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 gets chosen to run for vice-president.
“But that’s a very serious, you’re saying that, they’re saying that she doesn’t qualify because she wasn’t born in this country.”
The reporter replied there was no question that Ms Harris was born in the US, simply that her parents might not have been legal permanent residents at that time.