BISMARCK, N.D. — As a reporter started to ask Donald Trump a question about Sen. Elizabeth Warren (D-Mass.) during a news conference  Thursday afternoon, the likely Republican candidate cut him off.

“Who? Pocahontas?” Trump said. “Pocahontas?”

Trump has repeatedly called the senator by this nickname, referencing the controversy over Warren claiming that she is of Native American descent even if the connection is distant and difficult to prove.

As he spoke, Nicole Robertson shouted from the audience: “That’s very offensive!”

Robertson, 41, is a member of the Cree nation and was credentialed for the news conference because she is a freelance writer who focuses on native issues. Earlier in the conference, she asked Trump about tribal sovereignty, and he told her he would have to look into the issue. About 5 percent of North Dakota residents are Native American, one of the largest concentrations in the country.

After her condemnation, Trump sarcastically said: “Oh, I’m very sorry about that.” He then dropped yet another “Pocahontas."

Trump said that Warren’s tweets attacking him rarely get attention until he engages in the conversation. He called her “highly overrated,” accused her of passing “very little legislation” and said that many Democrats can’t stand her, including Democratic front-runner Hillary Clinton — even though Warren has become one of Clinton’s most outspoken advocates. Trump noted that he won the Republican primary in Warren’s home state of Massachusetts.

Then he tried to explain his use of the nickname that Robertson found offensive.

Trump said Warren has been unable to document her Native American heritage, and he impersonated Warren pointing to her high cheekbones as evidence. During a 2012 debate, Warren was asked about her ancestors, and she referenced her grandfather’s cheekbones.

“I don’t know if you would call it a fraud or not, but she was able to get into various schools because of the fact she applied as a Native American and probably able to get other things,” Trump said. “I think she’s as Native American as I am. Okay? That I will tell you.”

Trump wrapped up his comments by saying: “She’s a woman that has been very ineffective other than she’s got a big mouth.”

Later in the day, Trump doubled down on his comments in a tweet: “I find it offensive that Goofy Elizabeth Warren, sometimes referred to as Pocahontas, pretended to be Native American to get in Harvard.”

Warren responded in a series of tweets, saying Trump needs to get his facts straight, as she did not attend Harvard.

"I'm a graduate of @UHouston and @RutgersU," Warren tweeted. She followed up: "If @realDonaldTrump means my job at Harvard, he can ask Charles Fried, Solicitor General for Reagan. He says loud & clear that’s a lie."

After the news conference, Robertson said she was offended by Trump’s comments.

“It’s absolutely ludicrous in this day and age that we’re recognized as high cheekbones, the stereotypes of what you would see in ‘Dances with Wolves,’ ” Robertson said, referencing the 1990 movie. “Pocahontas — it’s so overdone. Like, come on. We’re living in a day and age now where that whole image and the romanticism around it and her portrayal — really it wasn’t a good story if you look at the history of Pocahontas.”

Robertson said that she would also be offended if Warren did in fact misrepresent her ancestry — but that it doesn’t excuse Trump’s use of “Pocahontas.”

“If she is Native American, all the best,” Robertson said.