President Trump repeatedly called Sen. Elizabeth Warren (D-MA) "Pocahontas" as an insult on the campaign trail, and he shows no signs of stopping.

During a White House event Monday honoring Native American code talkers — who helped the US in its communication strategy during World War II — President Trump used the event to take another jab at Warren without directly referring to her.

"I want to thank you because you're very, very special people," he said to the veterans. "You were here long before any of us were. Although we have a representative in Congress who, they say, was here a long time ago. They call her 'Pocahontas.'"

"Pocahontas" has apparently become Trump’s favorite nickname for Warren, who has said that she had Cherokee ancestors. Trump used the insult numerous times on the campaign trail, including at a chaotic rally in Albuquerque, New Mexico, in an interview with New York Times columnist Maureen Dowd, in a meeting with a group of senators in early 2017, and more than once on Twitter.

Pocahontas is at it again! Goofy Elizabeth Warren, one of the least productive U.S. Senators, has a nasty mouth. Hope she is V.P. choice. — Donald J. Trump (@realDonaldTrump) June 10, 2016

Trump's use of this particular nickname combines several of his worst habits: his inability to let perceived insults slide, his bullying mockery of opponents — and most of all, his general cluelessness on race issues.

This is just the latest example of Trump saying something blatantly racist

Trump has decades of racist statements and behavior under his belt. He has a particularly bad habit of essentializing people based on their heritage or ethnicity. Just look at his repeated comments alleging that federal judge Gonzalo Curiel, who presided over two class action suits against Trump University, is biased against Trump because of his Mexican heritage. (Curiel is American, born in Indiana to Mexican immigrants.)

Or look at Trump's "birther" conspiracy theories about President Obama, which helped Trump rise to political prominence in the first place. Or his seeming inability to talk about black people without also mentioning the "inner city."

Conflating all Native Americans with "Pocahontas" is another example of Trump's racist habits.

"Trump’s inability to discern the difference between Sen. Warren and Pocahontas is no accident," Cherokee Nation citizen Mary Kathryn Nagle told MSNBC's Adam Howard. "Instead, his attack on her native identity reflects a dominant American culture that has made every effort to diminish native women to nothing other than a fantastical, oversexualized, Disney character."

Debra Haaland, the first Native American State Democratic Party Chair of New Mexico, writes:

Trump’s very use of Pocahontas’ name is disrespectful. The story of Pocahontas is heart-wrenching. Toward the end of her life she left her people, went to England, contracted a disease and died at a very young age. When I think of that story — and the hundreds of sad and disturbing stories of how Native people have suffered throughout history, I can’t imagine making a mockery of their names or their lives. In my culture, we have deep respect for our relatives who have gone before us. It would be an utter disgrace to carry on as Donald Trump has about a Native woman whose life was cut short in a terrible way.

Why is Trump using this nickname for Warren?

Trump’s comments may be racist against Native Americans, but he’s using it here to sarcastically suggest that Warren really isn’t Native American. (Which, oddly enough, proves that Trump can also be racist while trying to insult someone for being white.)

Trump is referring to a controversy Warren faced over her ancestry during her 2012 Senate campaign.

Warren says she grew up being told that she had Cherokee heritage. "Everyone on our mother’s side — aunts, uncles, and grandparents — talked openly about their Native American ancestry," she wrote in her 2014 book, A Fighting Chance. "My brothers and I grew up on stories about our grandfather building one-room schoolhouses and about our grandparents’ courtship and their early lives together in Indian Territory."

This became an issue during her campaign when reports emerged that Harvard had once touted her Native American heritage as proof of its faculty's diversity. Warren, however, couldn't produce definitive proof of her Cherokee ancestry, and neither could genealogists.

This led to speculation that Warren had been a fake "diversity hire," or that she had abused the affirmative-action system to gain an advantage over other candidates.

However, as Garance Franke-Ruta reported for the Atlantic in 2012, there's no evidence that Warren ever used claims of Native American ancestry to help her get a job.

While Warren was listed as a minority in the Association of American Law Schools Directory of Faculty, she had declined to apply as a minority to Rutgers Law School, and had listed herself as "white" while teaching at the University of Texas. The head of the committee that recruited Warren to Harvard also said he had no memory of her Native American heritage ever coming up, and the 1995 Harvard Crimson article reporting on her tenure made no mention of it.

It's true, Franke-Ruta learned, that Warren wouldn't meet the criteria to officially qualify as Cherokee. She only claimed to be 1/32 Cherokee, which is too little to qualify for citizenship in two of the three major Cherokee tribes. She also doesn't have a known direct ancestor listed on the Dawes Rolls, which is a strict requirement for membership in the Cherokee Nation, or on the Baker Rolls, a requirement of the Eastern Band of Cherokee Indians.

But just because Warren can't find hard evidence of Native American heritage doesn't mean she doesn't have any, Franke-Ruta said — and even if she doesn't, that wouldn't make her a liar. Hazy oral histories about Native heritage are especially common in Oklahoma, where Warren grew up, and she would have no particular reason to disbelieve the stories she was told growing up.

Franke-Ruta notes that the shaky reliability of oral history has confounded other public figures — like Madeleine Albright, who didn't know until reporters discovered it that her own parents had escaped the Holocaust, or Marco Rubio, who mistakenly believed that he was the "son of exiles" from Castro's Cuba when his parents actually came over before Castro took power.

Trump sometimes uses racist attacks to distract from substantive critiques against him

Trump ultimately settled the Trump University lawsuits for $25 million. They were a major public relations problem for Trump, given damning evidence from documents and testimony from former students that the university was a fraudulent scam that deliberately preyed upon financially vulnerable victims.

That may have played into Trump's attacks on Curiel — and on Warren, who drew plenty of attention to the scandal during the campaign.

During one September CNBC interview in which Trump called Warren "Pocahontas," he also made some baffling statements about financial issues — casually lying about whether he personally invests in the stock market, and demonstrating that he knows nothing about how monetary policy works.

But Trump also launches personal attacks like this as a matter of course — and while he gives plenty of nicknames like "Little Marco" to his male opponents, he seems especially eager to insult women who he feels have wronged him.

Warren has been one of the Democratic party's most vocal critics of Trump, and she recently got a lot of media attention for being silenced on the Senate floor while criticizing Trump's attorney general nominee. So it's not surprising to see Trump try yet again to take her down a peg.