WASHINGTON (CBS) – Sen. Elizabeth Warren, of Massachusetts, apologized on camera Wednesday following a new report about her claims of Native American heritage.

The Washington Post reported Tuesday that Warren listed her race as “American Indian” on a State Bar of Texas registration card in 1986.

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Warren told reporters “I am not a tribal citizen” and recounted a conversation with Cherokee National Principal Chief Bill John Baker.

“I told Chief Baker that I am sorry that I extended confusion about tribal citizenship and tribal sovereignty and for harm caused,” she said. “I am also sorry for not being more mindful of this decades ago. Tribes and only tribes determine tribal citizenship.”

Warren is exploring a run for the White House. President Donald Trump has repeatedly labeled her “Pocahontas” as a result of the heritage controversy.

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In October, Warren released a DNA test reportedly showing that a Native American relative appears in her family tree 6 to 10 generations ago. The test did not silence critics and the Cherokee Nation has called using DNA tests to lay claim to Native American heritage “inappropriate and wrong.”

The Cherokee Nation said last week that Warren has apologized for the DNA test.

Sen. Elizabeth Warren (CBS News)

“There’s no doubt about it, this is becoming politically toxic for her,” WBZ-TV’s Jon Keller said.

Despite this being the scandal she can’t separate from, there’s no real evidence Warren used what she believed to be her heritage to gain advantages in her career. Still, Keller says the distraction can be damaging.

“However fact-free this miasma of speculation about her integrity renders her as unlikely to do as well in a possible match up with Trump as some other candidates, it’s a problem,” Keller says. “There’s no getting around it.”

Last September, Boston Globe reporters found no trace of favorable treatment because of the heritage claims. They also found employers were mostly unaware of her heritage during the hiring process.

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The prospective 2020 Democratic presidential candidate is expected to formally announce her entrance into the race on Saturday.