When Sen. Elizabeth Warren released DNA test results asserting her Native American ancestry this week, she was blasted by tribes including the Cherokee Nation, whose leader called genetic tests "useless" for determining tribal citizenship.

Whether the Massachusetts Democrat realized it or not, she had stumbled into a long-running debate about Native American identity. Her announcement of evidence for her ancestry claims, and the swift backlash from some tribal leaders, shined a national spotlight on the question of who can claim citizenship in an indigenous tribe. It's an issue with a fraught and complex history, and one on which citizens of America's over 560 federally recognized tribal nations do not speak with a single voice.

Jamie Azure, a tribal leader in North Dakota, was glad to see Warren, who faces re-election next month, embrace her heritage. He believes Native Americans need to be more accepting of those who want to get in touch with a piece of their ancestry, no matter how small, rather than enforcing stringent standards on who belongs.

"It made me feel proud to see her talking about it," Azure said. "She's proud to have it in her blood."

But Twyla Baker, an educator and citizen of the Three Affiliated Tribes of North Dakota, criticized Warren for claiming a Native American identity based on DNA test results, which are not specific enough to show a connection to a particular tribe or even to North America's indigenous peoples.

Warren's "types of claims can damage the validity and work of indigenous people who are living their identities every day," Baker said. "It also lays the groundwork to do serious damage to our sovereignty, as tribes are responsible for defining who is a tribal citizen."

Cherokee Nation Secretary of State Chuck Hoskin Jr. agreed. "Senator Warren is undermining tribal interests with her continued claims of tribal heritage," he said in a statement.

In response, Warren told The Boston Globe that she should have better emphasized that she has never claimed Native American citizenship.

"There's a distinction between citizenship and ancestry," Warren said. "I wish I had been more mindful of that distinction. The tribes and only the tribes determine citizenship."

ANCESTRY VERSUS IDENTITY

After centuries of racial genocide committed against indigenous peoples by European settlers, tribes in the U.S. have fought for the legal authority to self-govern, which includes determining standards for who belongs.

Today, many Native Americans define their identity based on their citizenship in a recognized tribe — not simply by tracing their identity through an ancestor or DNA test, said Krystal Tsosie, an indigenous Native American geneticist who is part of the Navajo Nation in Arizona.

"We as Native Americans are just concerned that people will start equating ancestry with identity," Tsosie said. "We feel this way because there was miscommunication with what Warren was trying to show and do. Individuals are trying to gain a sense of belonging in our communities when they haven't lived with our ways and in our communities."

"It's not for an outsider to proclaim themselves as Native Americans," she added. "That's currently the discussion that many members are having about non-Natives."

Tsosie's Navajo Nation is one of dozens of tribes that require a person seeking citizenship to show a certain percentage of their familial ties are from that tribe. That is determined with the help of historic records and documentation through the Bureau of Indian Affairs, and is known as a blood quantum standard. This is different from DNA testing, which may not capture a full genetic picture of a person's ancestors.

Other tribes do not use a blood quantum standard and instead use an open enrollment system with requirements that may include community service within the tribe.

Warren's assertion of Native American ancestry has rankled people such as Nick Estes, an assistant professor of American studies at the University of New Mexico and citizen of the Lower Brule Sioux Tribe in South Dakota.

After centuries of colonial and racial-based oppression, for anyone "to claim Native American [ancestry] trivializes indigenous people and is not something to be taken lightly," Estes said.

WARREN'S HERITAGE

Warren identifies as white but grew up in Oklahoma believing that her mother's side of the family had Cherokee and Delaware blood.

Doubts surrounding Warren's ancestry were raised during the 2012 Senate race, when Republican opponent Scott Brown claimed she dishonestly listed herself as Native American to advance her career as a faculty member at the University of Pennsylvania Law School and later, Harvard Law School. While Warren had been listed on forms at Penn as a Native American, she said she couldn't remember asking for that distinction.

The Boston Globe published a report last month that found Warren's claim to Native American ethnicity was never considered by the Harvard Law faculty and those responsible for hiring viewed her as a white woman.

Trump began criticizing Warren's claims to Native American heritage during the 2016 campaign and has repeatedly mocked her at rallies this year as she appears to be a contender in the 2020 presidential race.

She said she released her DNA test as ammunition against the ridicule, but Trump this week lampooned the results: "She owes the country an apology. What is the percentage? One one-thousandth?"

IDENTITY BEYOND BLOOD

Gabriel Galanda, a Seattle lawyer with the Round Valley Indian Tribes of California, wasn't bothered that Warren took a DNA test. If anything, he said, doing so has shown how some tribes continue to be too stringent in requiring documentation of ancestral links.

"Horrifically, today we indigenous peoples are using race as weaponry to self-extinguish ourselves," said Galanda, whose firm has represented people removed from tribal enrollment based on their lineage. (The New York Times reported last year that cases of disenrollment remain most prevalent in smaller tribes with casinos, where profits go a longer way among fewer citizens.)

Galanda estimates that 80 tribal nations have moved to disenroll citizens.

"Federal racial metrics for tribal belonging have supplanted Indian kinship teachings in too many communities," Galanda said. "To me that is a far, far bigger concern than Senator Warren's ancestry or DNA test results."

The Mashpee Wampanoag of Massachusetts, which became federally recognized in 2007 and has about 2,600 enrolled citizens, does not use a blood standard for membership. Instead, people have to prove they are descended from one of the 451 Indians who were living in the Mashpee Indian District before the present-day town of Mashpee became incorporated.

In addition, said Brian Weeden, a tribal youth council adviser, all citizens must be actively involved in the community. Weeden has spent this week getting people to register to vote in time for the November election. Among those who signed up is Troy Stewart, 19, his cousin.

Stewart, who identifies as Native American and African-American, said he and most people he knows in the tribe plan to vote for Warren. The way the president has taunted her over her heritage has upset many, he added.

Warren visited the tribe last April to shake hands and tour their health center.

"Whether she claims to be Native American or belongs to a certain tribe or not is irrelevant to me," Stewart said. "As long as she says, 'Hey, I've met with them, I've learned about them, and their tribes are something we need to protect' — that's what I really care about."