The notion that politicians whose parents are immigrants can’t serve in high office has racist roots. But it’s one President Trump can’t resist, first with former president Barack Obama, and now he’s indulging it with Joe Biden’s vice-presidential pick, Sen. Kamala D. Harris (D-Calif.).

Almost immediately after Biden announced Harris as his running mate, a theory picked up steam on the right that Harris can’t serve as vice president because her parents were born abroad. A conservative law professor wrote in a Newsweek opinion piece that this poses a “challenge to Harris’ constitutional eligibility.”

Harris’s mother is from India and her father from Jamaica. Harris was born in Oakland, Calif. She is a natural-born citizen, which means she meets the requirements to be president or vice president. But similar to the last non-White person on a presidential ticket, she faces baseless theories that she’s ineligible.

Trump legal adviser Jenna Ellis shared the Newsweek article on Twitter earlier Thursday. Then, at a coronavirus briefing at the White House on Thursday, a reporter asked Trump what he thought about it. Rather than disavow it or even distance himself from it, Trump breathed life into the notion. Here’s what he said:

So I just heard that. I heard it today that she doesn’t 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 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 explained that Harris was born in the United States; her parents weren’t. Trump responded: “I don’t know about it. I just heard about it. I’ll certainly take a look.”

The Washington Post’s Fact Checker granted Ellis and Trump four Pinocchios for these claims.

Trump didn’t outright say Harris couldn’t serve, but he left the question out there. And as we saw with the rumors he propagated about Barack Obama’s eligibility, raising questions is enough to fuel suspicions. Trump was the most prominent conspiracy theorist on Obama, seeking publicity to fuel the false rumors that Obama wasn’t born in the United States. It wasn’t until the very end of the 2016 election when he somewhat reluctantly said at a campaign event: “President Obama was born in the United States. Period.” (And then he accused Hillary Clinton’s campaign of starting the rumor.)

The Obama birther movement was Trump’s biggest foray into the political world, as he toyed with running for president. When he was running for president, he questioned whether his Republican opponent, Sen. Ted Cruz (R-Tex.), could serve because he was born in Canada. Now that Trump is president, it’s not clear whether questioning Harris’s qualifications is a strategy or something that was thrown at him that he latched on to.

But it’s certainly politically questionable.

Trump’s instincts to attack his opponents in racial and gendered ways aren’t serving him in the polls right now. He is trailing Biden substantially in national polls and key swing states, and that’s primarily because Americans disapprove of his handling of the coronavirus pandemic. But Trump’s handling of the protests of racial injustice this summer has also hurt his reelection chances. Rather than make an effort to empathize with the protesters, whose cause a majority of Americans support, he spent more energy trying to demonize the protesters as radical.

Now, a number of Republicans and Republican strategists worry that Trump is pushing away suburban voters (who are increasingly diverse) with his rhetoric on protests and race.

The numbers show why. A Washington Post-ABC News poll in July found that Biden has a 25-point advantage over Trump when it comes to who is better suited to handle race relations, and Trump has lost ground with White women, who are also seen as a key swing demographic and whom he won in 2016.

As The Post’s David Weigel points out, Democrats are enjoying, to a degree, the Trump campaign talking up theories about Harris’s eligibility. It means they’re not spending time attacking her on policy. And Republicans have yet to even find a clear strategy for that, accusing her of being both too liberal and not populist enough.