(CNN) Before and after his election, President Donald Trump has sneeringly referred to Massachusetts Sen. Elizabeth Warren as "Pocahontas" as a way of mocking her claim to some sliver of Native American heritage.

At a rally in Montana earlier this year, he called on her to take a DNA test (something former GOP Massachusetts Sen. Scott Brown, defeated and unseated by Warren in 2012, suggested in 2016) and even made her a memorable offer.

"I will give you a million dollars to your favorite charity, paid for by Trump, if you take the test and it shows you're an Indian," Trump said. "I have a feeling she will say no but hold it for the debates."

He was wrong.

On Monday, Warren revealed that an analysis of genetic testing confirmed her distant Native American ancestry. Trump shrugged off the news and denied he made the big dollar wager.

So how did this become an issue -- one Trump has pressed and Warren, as she prepares for an expected 2020 presidential run, has sought to defuse -- and what are the basic, underlying facts?

Here's a quick look.

Is Warren part Native American?

Warren has long said that she is pointing to "family stories" passed down to her through generations as evidence.

On Monday, Warren cited and publicized analysis from Carlos Bustamante, a professor of genetics at Stanford and adviser to Ancestry and 23 and Me.

"While the vast majority of the individual's ancestry is European," he concluded of Warren, "the results strongly support the existence of an unadmixed Native American ancestor in the individual's pedigree, likely in the range of 6-10 generations ago."

In short, the results pretty much agree with what Warren has been arguing for years.

"I am very proud of my heritage," she 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.

The Washington Post's "Fact Checker" page, in a piece from June 2016, actually decided against judging the issue at all, offering "no rating" and 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, and an in-depth investigation by the Boston Globe , published on September 1, found the same.

"At every step of her remarkable rise in the legal profession," the report read, "the people responsible for hiring her saw her as a white woman."

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.

"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 during the 2016 campaign that Warren "take a DNA test" to prove she's part Native American.

What's been Trump's line of attack?

Mostly name-calling 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 tweeted in May 2016.

Trump sharpened his attacks as that campaign heated up, 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."

"I hope that she's selected as the vice presidential running mate. I will speak very openly about her if she is," he said at the time.

Warren shot back, tweeting: "If you think recycling Scott Brown's hate-filled attacks on my family is going to shut me up, @realDonaldTrump, think again buddy. Weak."

The fundamentals haven't changed much over the past two years. Warren has emerged as one of Trump's sharpest critics and a top 2020 contender. Trump has routinely peddled the "Pocahontas" line, in speeches and on Twitter.

And who was Pocahontas anyway?

Pocahontas, the daughter of a Native American chief, welcomed English settlers to the current-day US 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."