During the 2016 election cycle, presumptive Republican presidential nominee Donald Trump has regularly questioned the background of Massachusetts Sen. Elizabeth Warren, who has said she has Native American heritage. But he's certainly not the first political opponent to question the progressive lawmaker's background.

At a North Dakota press conference Thursday, Trump lobbed his latest insult at Warren, sarcastically calling her "Pocahontas." In March, he called Warren "the Indian" after the senator went on a Twitter rant about the bombastic billionaire. 

Trump has rekindled a line of attack against Warren that began in 2012 when she was running against then-Republican Sen. Scott Brown. He openly questioned Warren's claims to Native American ancestry, saying she used it for a career boost.

Warren's claims to a Native American background first came up years before, when she was teaching at Harvard Law School. "In late April, the Boston Herald reported that in the 1990s, Harvard Law School — where Warren began teaching in 1992 and was granted tenure in 1995 — touted the Democrat’s Native American background as part of an effort to boost its diversity hiring record. Warren’s campaign said she didn’t bring up her heritage before Harvard hired her and that her background came out through later conversations," the Washington Post wrote in 2012.

Warren was listed as a minority professor at Harvard and at some point informed the University of Pennsylvania she was Native American while working there, as well. But in an application to Rutgers Law School in New Jersey she reportedly did not apply as a minority student, and she listed herself as "white" while teaching at the University of Texas.  

Brown in 2012 pressed for documentation proving Warren's background during the 2012 race, but Warren never provided any. The senator is reportedly 1/32 Cherokee, but that would not qualify her to be a member of the tribe, according to Yahoo News. Warren has in the past talked about family stories to defend her Native American heritage and at one point referenced "high cheekbones" in a somewhat convoluted answer. 

"I have lived in a family that has talked about Native America, talked about tribes, since I’ve been a little girl," she said in 2012, according to the Washington Post. "I still have a picture on my mantle at home, and it’s a picture of my mother’s dad, a picture of my grandfather. And my Aunt Bee has walked by that picture at least a thousand times, remarked that her father, my Pappa, had high cheekbones, like all of the Indians do, because that’s how she saw it. And your mother got those same great cheekbones, and I didn’t."

Trump brought up that high-cheekbone reference Thursday in North Dakota. "'Well, I have high cheekbones. You see I have high cheekbones, so I'm a Native American,'" he said, seeming to mock Warren. "I don't know if you would call it a fraud or not, but she was able to get into various schools because she applied as a Native American. I think she's as Native American as I am, OK? That I will tell you."

While Warren's background has long been a point of contention, the Atlantic talked with a genealogist who pointed out in 2012 that people with Cherokee heritage can look like Warren. The piece read, in part: "None of this is to say that a Cherokee citizen couldn't look like Warren. Though it confounds many people's expectations, the Cherokee Nation considers being Cherokee as much an ethnicity as anything racial, and given the tribe's centurieslong history of intermarriage there are many Cherokee citizens today who do not look stereotypically Native American. As well, 'there are a lot of folks who are legitimately Cherokee who are not eligible for citizenship,' said Krehbiel-Burton, because, for example, their ancestors lived in distant states or territories when the rolls were drawn up or because they are direct descendants of people left off the rolls for other reasons."