Sioux City, Iowa (CNN) Sen. Elizabeth Warren was confronted by a voter in Sioux City on Saturday morning over her controversial decision to use a DNA test to prove her claims to Native American ancestry.

"I am not a person of color," the Massachusetts Democrat said. "I am not a citizen of a tribe. Tribal citizenship is very different from ancestry. Tribes -- and only tribes -- determine tribal citizenship, and I respect that difference."

Warren has addressed the backlash to her DNA test before, using similar language, but this -- the first question on her first full day of campaigning for the Democratic presidential nomination in Iowa -- underscored the lingering concerns over her decision.

The logic behind it, Warren explained, was simple. She grew up in Oklahoma, and like so many others in that region of the country, had been told of her family's Native American roots. The controversy traces back years, and more than one election, she said, recalling that her claim had been used against her by Republicans during her successful 2012 Senate campaign.

"My decision was to put it all out there," Warren said of the final calculation this time around.

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