(CNN) -- Writer Mark Trahant guessed the situation was a first: dueling senatorial campaign ads that centered on a candidate's Native American roots.

He was referring to the Senate race in Massachusetts that pits Harvard University law professor Elizabeth Warren against Republican Sen. Scott Brown.

There are many issues of contention in this hotly contested race, but one of them has become Warren's claim to Native American ancestry. After Brown accused her of taking advantage of minority status, Warren fired back in an ad that accused Brown of attacking her family.

"As a kid, I never asked my mom for documentation when she talked about our Native American heritage," Warren says in the spot. "What kid would? But I knew my father's family didn't like that she was part Cherokee and part Delaware, so they had to elope.

"Let me be clear: I never asked for or never got any benefit because of my heritage," she continues, addressing the central concern that Brown has brought up on the campaign trail and at the candidates' first debate last week. "The people who hired me have all said they didn't even know about it."

It's a bit more complicated, said Trahant, a member of the Shoshone-Bannock Tribes.

"The usual standard is citizenship, being a member of a tribe. Elizabeth Warren does not meet that test," he said.

"It's not right that she would use her self-recalled heritage for any academic advancement ... even if there are no academic standards that define who is legally a Native American (except the citizenship issue). On the other hand, when you see videos like this one, you cringe."

He was referring to a video that shows Brown staffers chanting war whoops and gesturing Tomahawk chops. It was posted Tuesday on YouTube by the liberal blog Blue Mass Group.

"I think Sen. Brown has some explaining to do about the nice guy, respectful tone that he sets in his office, and on his campaign," the blog said. "And maybe we can put this whole preposterous issue to bed once and for all."

Brown responded to CNN affiliate WCVB in Boston.

"It is certainly something that I don't condone," he 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."

Elizabeth Warren vs. Scott Brown: Priciest race this year

The debate about Warren has gone on since May, when Warren confirmed that she had described herself in faculty directories as having Native American blood. She said she did it to meet others like her.

But her explanation didn't sit well in some corners.

A website called Cherokees Demand Truth From Elizabeth Warren says Americans ought to care deeply about such claims.

"America should care because they care when someone falsely claims to be a decorated military veteran. They care when someone falsely claims to be a recovering drug addict in a book passed off as the truth. And they care when someone falsely claims to be a survivor of the Jewish Holocaust. America cares about these things because America cares about integrity, honesty and fair treatment.

"Elizabeth Warren has not just stolen an ethnic identity that does not belong to her, but she has also personally benefited from it and harmed the integrity of the American ethos of advancement based on quality of work, not color of skin."

The New England Historic Genealogical Society provided initial research that shows several members of Warren's maternal family claiming Cherokee heritage. Warren's great-great-great grandmother O.C. Sarah Smith, is said to be described as Cherokee in an 1894 marriage license application. The genealogical society gathered that information through a 2006 family newsletter and said the original application cannot be located.

Warren's critics were out in force Tuesday on Twitter, including Francesca Chambers, the editor of the conservative Red Alerts Politics website.

"When you have to release an ad explaining why you think you're a Native American, it's not good," she tweeted.

Blogger Donny Furguson posted: "If Elizabeth Warren can fake four more identities she'll start touring as The Village People."

But Warren was not without her supporters.

Seroe Michaud commented on Native News Network's page:

"Good for you Elizabeth, I am 1/8 Blackfoot but am fair skinned and light haired, I am the only light one in the family. If like me your blood is part native on your mother's side and your heart is walking the red road, we will not be driven into the shadows. I hope that you win, you had my vote before I learned of your roots."

As Trahant said, it's complicated.

What makes someone "legitimately" Native American? And who gets to make the call? CNN attempted to answer those questions when the Warren controversy erupted.

Julia Good Fox, professor of American Indian studies at Haskell Indian Nations University, said there's plenty of ignorance around Native American citizenship.

"It's all in past-tense, and we don't get a sense of what an Indian today looks like," she said in May.

And that, she said, can be confusing.