During an interview at the National Association of Black Journalists annual convention this week, Donald Trump drew audible gasps from the crowd when he questioned the background of Vice President Kamala Harris, the presumptive Democratic nominee for president.

I didnt know she was Black until a number of years ago, when she happened to turn Black, and now she wants to be known as Black, the former president said about Harris . So, I dont know, is she Indian or is she Black?

She was Indian all the way and then, all of a sudden, she made a turn and she went, she became a Black person, Trump added. I think somebody should look into that.

Harris father is a Jamaican immigrant and her mother was an Indian immigrant. She attended Howard University, a prestigious historically Black university in Washington, D.C., where she pledged Alpha Kappa Alpha, a Black sorority.

Democrats were quick to condemn Trumps comments, and many Republicans struggled to defend him .

But this attack line against Harris wasnt a slip of the tongue or a product of an undisciplined politician. Questioning the identity of Black politicians is what made Trump into a Republican darling, and later the partys standard-bearer.

There are parallels between this and his attacks on Barack Obama, said Donald Earl Collins, a critical race, gender and culture studies professor at American University. Its about going after voters who have problems with [candidates] identities.

Trump infamously and baselessly claimed that Obama, who was born in Hawaii to a Kenyan father and white American mother, was not an American and therefore ineligible to be president. He spent years rallying conservatives around the so-called birtherism theory, pushing for Obama to publicly release his long-form birth certificate.

The fact that Trump was invited to NABJ, a space for Black journalists to connect and network, was controversial. During his interview with three prominent Black women journalists Rachel Scott of ABC, Kadia Goba of Semafor and Harris Faulker of Fox News he reportedly refused to be fact-checked, thus holding up the event. Trump relied on his same old talking points, yet called Scott rude and nasty for daring to ask him about his past comments. He lied about Democrats views of abortion and stumbled over questions about the Jan. 6, 2021, insurrection.

And he used the fact that Harris is biracial to attack her.

Being mixed race is a simple concept, and according to 2020 census data, approximately 10% of Americans identified as having more than one race. So why is Trump acting like Harris identity is confusing or something shes lying about?

What Trump is attempting to say is, She doesnt meet your litmus test for being truly Black, Collins said.

The question of who is Black has ties to Americas long history of racism, from slavery to segregation. Some mixed-race people in the United States are descended from both white slave owners and the enslaved women they raped . During the Jim Crow era, the one drop rule (meaning one drop of Black blood) was used to determine who was Black and therefore segregated from whites-only spaces, leading some Black people to pass as white in an attempt to avoid discrimination.

Although Trump may not understand all of this history, Collins said that he understands enough to know because Harris is mixed-race, highly educated and a woman, he can claim shes not really Black.

While some Republicans tried to dodge the issue of Trumps comments altogether, others dutifully fell in line.

Trumps running mate, Sen. JD Vance (R-Ohio), said Trump was right to question Harris race.

Look, all he said is that Kamala Harris is a chameleon, Vance told CNN . She is everything to everybody, and she pretends to be somebody different depending on which audience she is in front of. I think its totally reasonable for the president to call that out, and thats all he did.

Vance is married to an Indian woman and has biracial children.

Rep. Lauren Boebert (R-Colo.) was also in agreement. President Trump is right, she tweeted . She switched.

Boeberts tweet included two screenshots of headlines from The Associated Press: one calling Harris the first Indian-American US senator, and one identifying her as the first Black woman to be a running mate in a presidential election. Conservatives have latched onto such headlines as proof that Harris didnt always identify as Black, ignoring the fact that the AP didnt call Harris the first Black senator because that title belongs to Hiram Revels, who was elected to serve in 1870.

Its unclear if the average voter has an appetite for such naked racism. But Trump isnt pivoting to birtherism 2.0 because he believes it will sway swing voters. Hes being who he has always been, which won him a strong GOP base and the White House.

What other cards does he have to play? Collins said. This is the one thing that he knows how to do.