Sen. Elizabeth Warren (D., Mass.) on Tuesday apologized for identifying herself as a Native American for nearly two decades, including on a previously undisclosed State Bar of Texas registration card where she listed her race as "American Indian."

"I can’t go back," Warren said during an interview with The Washington Post. "But I am sorry for furthering confusion on tribal sovereignty and tribal citizenship and harm that resulted."

Her apology comes amid an ongoing controversy that has lasted over a year and has been haunting her 2020 candidacy as she prepares to formally announce a presidential bid.

In addition to releasing her DNA results last October, stirring backlash with Native Americans and progressives, she released employment documents last summer. She also gave a speech last year discussing her reasons for why she called herself a Native American, but she didn't apologize. Warren, who announced she was forming a presidential exploratory committee in December, could see additional documents surface to keep the issue alive, according to the Post.

The Post, for example, used an open records request during a general inquiry to obtain Warren’s 1986 registration card for the State Bar of Texas, which showed she identified as an "American Indian."

Warren filled out the card in April 1986 using blue ink, making it the first document to show her claim using her own handwriting. Warren's office did not challenge the authenticity of the registration card. In addition to her apology to the Post, it was previously reported that Warren called Bill John Baker, the principal chief of the Cherokee Nation, to apologize for the release of her DNA test:

Julie Hubbard, a spokeswoman for the Cherokee Nation, declined to address the scope of the conversation between Warren and the chief. Warren, asked in a brief interview Tuesday if she’d intended the apology to include labeling herself as Native American when at the University of Pennsylvania and at Harvard University, replied "yes." She gave the same response when asked if it included labeling herself as a minority in the Association of American Law Schools directory. "I told him I was sorry for furthering confusion about tribal citizenship," Warren said. "I am also sorry for not being more mindful about this decades ago. We had a good conversation." CNN reported her broader apology on Monday. The apology has met with mixed reactions. Several tribal members applauded her. "This closes the matter," tweeted Keith Harper, a citizen of the Cherokee Nation and a former U.S. ambassador to the U.N. Human Rights Council. "Onward."

While some tribal members applauded her, David Cornsilk, who is a citizen of the Cherokee Nation, said that he wanted to see an apology in writing and on television.

"I want her to go on national TV. I want her to do a video like she did to announce her DNA results. It just seemed very lacking," Cornsilk said.

Warren released her DNA results in October in attempt to put to rest criticism she's faced for years over her claim to Native American identity. The test showed she had a distant Native American ancestor, and the move backfired when Cherokee leaders slammed her for using a test to show a tribal relationship, according to the Post: