"Is Warren part Native American?
Warren says, yes, she is, and points to "family stories" passed down to her through generations as evidence.
"I am very proud of my heritage," Warren told NPR in 2012. "These are my family stories. This is what my brothers and I were told by my mom and my dad, my mammaw and my pappaw. This is our lives. And I'm very proud of it."
In that account and others, a genealogist traced Warren's Native American heritage to the late 19th century, which, if true, would make her 1/32 Native American. (However, the legitimacy of those findings has been debated.)
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The Washington Post's "Fact Checker" page has actually decided against judging the issue at all, offering "no rating" and, in a piece Tuesday, suggesting "readers to look into it on their own and decide whether Trump's attacks over Warren's background have merit."
Did it play a role in her career?
Harvard Law School in the 1990s touted Warren, then a professor in Cambridge, as being "Native American." They singled her out, Warren later acknowledged, because she had listed herself as a minority in an Association of American Law Schools directory. Critics note that she had not done that in her student applications and during her time as a teacher at the University of Texas.
Warren maintains she never furthered her career by using her heritage to gain advantage.
Trump: Elizabeth Warren is "very racist"
How did this become a political issue?
It began during Warren's 2012 Senate run, when her opponent, Brown, accused her of lying to get a leg up in her academic career.
"Professor Warren claimed that she was a Native American, a person of color," he said during a debate. "And as you can see, she's not."
Warren shot back that she had not gained any "advantage" -- a claim that has proven impossible to fact check -- and in a subsequent ad again cited family lore.
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"As a kid, I never asked my mom for documentation when she talked about our Native American heritage. What kid would? But I knew my father's family didn't like that she was part Cherokee and part Delaware, so my parents had to elope," she said.
Their quarrel took a nasty turn around this time, when Brown's staffers were filmed doing "war whoops" and "tomahawk chops" during an outdoor rally.
Brown told WCVB in Boston that he didn't condone their actions, but said "the real offense is that (Warren) said she was white and then checked the box saying she is Native American, and then she changed her profile in the law directory once she made her tenure."
Warren's earlier musings on the "high cheekbones" of certain close family members didn't exactly satisfy the skeptics (and made some allies wince).
Brown, a surrogate for Trump, suggested Monday that Warren "take a DNA test" to prove she's part Native American.
What's been Trump's line of attack?
Mostly namecalling and trying to use Warren's statements about her heritage to discredit her.
"Let's properly check goofy Elizabeth Warren's records to see if she is Native American. I say she's a fraud!" he had tweeted last month.
Trump sharpened the point Monday, telling NBC News: "She made up her heritage, which I think is racist. I think she's a racist, actually because what she did was very racist."
Trump: Elizabeth Warren is "as Native American as I am"
"I hope that she's selected as the vice presidential running mate. I will speak very openly about her if she is," he said. "She is one of the least productive senators in the United States Senate. We call her 'Pocahontas' for a reason."
Warren didn't back down.
"If you think recycling Scott Brown's hate-filled attacks on my family is going to shut me up, @realDonaldTrump, think again buddy. Weak," she replied.
And who was Pocahontas anyway?
Pocahontas, the daughter of a Native American chief, welcomed English settlers to the current-day U.S. in the early 17th century. Legend holds that she saved the life of Captain John Smith, stopping his execution by laying her head upon his.
Years later, though, she was kidnapped by another group of English and in 1614 converted to Christianity while in captivity before marrying a tobacco farmer and taking the name "Rebecca." "