BOSTON (CBS) – Senator Brown used the first question of Thursday’s Massachusetts US Senate debate on WBZ-TV to go after opponent Elizabeth Warren’s claims of Native American ancestry.

When asked whether character is an issue in the race, Brown came out swinging, calling on Warren several times to release her personnel records from Harvard University.

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“I think what you’re referring to is the fact that Professor Warren claimed that she was a Native American, a person of color, and as you can see, she’s not,” he said. “When she applied to Penn and Harvard, she checked the box claiming she was a Native American. Clearly she’s not. That being said, I don’t know, and neither do the viewers know whether she got ahead as a result of checking that box.”

Brown suggested the burden of proof was on Warren, and the only way she could prove that she didn’t have an advantage of minority status was by releasing her records.

“You refuse to release your records, and I think that speaks volumes,” Brown said.

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Warren defended her ancestry claim with the repeated assertion that her fathers’ family wouldn’t allow her parents to marry because of her mother’s Native American heritage. Warren said she had no reason to question her family’s claims, and denied ever using the claims to get ahead.

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“This is my family, this is who I am and it’s not going to change,” she said.

“When I was growing up, these are the stories I knew about my heritage. I believed my mother and my father and my aunts and my uncles,” she said. “I never used it, never used it for getting into college, never used it for getting into law school, and the people who have hired me for my jobs have all made it clear that they didn’t even know about it until long after I was hired.

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For several months, Brown has made a campaign issue out of questioning Warren’s credibility by repeatedly accusing her of misrepresenting her heritage.