President Trump, in an echo of his false birtherism claims against President Barack Obama, said Thursday that questions about the eligibility of Sen. Kamala D. Harris to run for vice president were “very serious” despite the fact that they are baseless.

Harris (D-Calif.) was born in Oakland, Calif., and is, by the laws of the Constitution, a U.S. citizen.

The false birther conspiracies about Harris focus on the status of her parents, immigrants from India and Jamaica, who weren’t U.S. citizens when she was born. Online speculation and far-right commentary on the matter gained traction Thursday, and a Trump campaign adviser was among those circulating material questioning Harris’s legitimacy.

Asked whether Harris was indeed eligible, Trump said he did not know and had only just heard of the issue.

“So I just heard that, I heard it today that she doesn’t meet the requirements,” Trump said during a White House news briefing.

He then added that “the lawyer that wrote that piece is a very highly qualified, very talented lawyer,” making clear that he had some familiarity with the assertions made by John C. Eastman, a conservative lawyer at Chapman University.

Eastman’s essay was promoted on Twitter by Tom Fitton, of the conservative legal group Judicial Watch, among others. A legal adviser to Trump’s reelection campaign, Jenna Ellis, tweeted Thursday Fitton’s link to Eastman’s essay on the matter, thus linking it directly to Trump.

By declining to refute the assertion fully, Trump amplified it.

“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,” Trump said, breaking off the thought.

“You’re saying that, they’re saying that she doesn’t qualify because she wasn’t born in this country?”

Trump said he would take a look at the question of Harris’s eligibility.

The president has long called for an end to birthright citizenship. Any person born in the United States, regardless of their parents’ nationality, is an American citizen under the 14th Amendment of the U.S. Constitution.

The Biden campaign sent a scathing statement in response to the president stoking the false conspiracy theory.

“Donald Trump was the national leader of the grotesque, racist birther movement with respect to President Obama and has sought to fuel racism and tear our nation apart on every single day of his presidency,” a Biden campaign spokesman said in an email. “So it’s unsurprising, but no less abhorrent, that as Trump makes a fool of himself straining to distract the American people from the horrific toll of his failed coronavirus response that his campaign and their allies would resort to wretched, demonstrably false lies in their pathetic desperation.”

Trump’s remarks were a reprise of his past false allegation that Obama was born in Kenya rather than in Hawaii and thus ineligible to serve.

Trump largely built his 2016 presidential campaign out of the political prominence he gained from questioning Obama’s legitimacy for five years.

Under pressure as the Republican nominee, Trump said in September 2016 that Obama “was born in the United States, period.”

Biden and Harris both referenced her parents’ immigrant stories and her own American life story during their first appearance as running mates Wednesday.