The Trumpian taunt is a trap. A video released by Senator Elizabeth Warren, of Massachusetts, on Monday demonstrates just how it works.

What Warren intended to demonstrate is that she has Native American ancestry, and that she has a genetic test to prove it. She did this because Donald Trump has repeatedly accused her of lying about her heritage and, during a rally last summer, even promised to donate a million dollars to the charity of Warren’s choice if she could produce a genetic test that verified her claims.

In addition to the video, Warren posted a geneticist’s report on her DNA test. It’s worth noting what the report said: not very much. The author of the report—the Stanford University professor Carlos Bustamante, who consults for several DNA-testing services—identifies Warren as a person of European ancestry and writes that more than ninety-five per cent of her genome comes from Europe. A small portion, he writes, appears to point to a distant Native American ancestor, between six and ten generations ago.

It is important to understand that, contrary to the impression created by television and online advertising, a DNA test can never provide definitive information about one’s heritage. Ancestry-testing services deal in correlations: they collect data on genetic markers on the one hand and personal narratives on the other. If all or most of the people who identify as, say, Ashkenazi Jewish have a certain genetic marker, the database will learn to recognize the marker as “Ashkenazi Jewish”; chances are, most Palestinians in this world would have this marker as well, but as long as none of them has used this particular service, the marker will be known as “Jewish.”

When ancestry-testing services first appeared in this country a dozen years ago, they found that Americans, at least, tended to have fairly reliable stories about their family heritage. An exception was people who had a family story, usually passed down through a number of generations, of having Native American blood—most often, the legend said that they were Cherokee. For years, geneticists had trouble finding any corroboration for this claim. It’s possible that their tests weren’t sensitive enough, or that they were looking in the wrong place; it is also possible that family stories of having descended from Native Americans were particularly unreliable. Over time, the tests learned to detect ever more subtle signs and patterns, as Warren’s case appears to have done.

Trump’s frequent attacks on Warren have contained several transparent messages. She looks like a white woman but she claims to be Native American, and therefore she is a liar, says one. In the Trumpian universe, lying is always motivated by profit; therefore, Warren must be lying because she wants the benefits of being Native American, as these must have to do with education and employment. Trump conjures so many familiar irritants: a woman, a cheater, someone nonwhite, and affirmative action itself. He has been demanding the DNA test the same way he used to demand that President Obama produce his birth certificate.

The senator’s video is carefully worded. Warren says that she is laying no claim to citizenship in a tribe. She frames her understanding of her ancestry in terms of experience, though this experience seems fairly well removed: the defining event in Warren’s family was her father’s family’s disapproval of his marriage to her future mother; Warren says that it was the Native American heritage that made her father’s family suspicious. Talking heads from the universities where Warren was employed assure the audience that she has never used her heritage to advance professionally.

Visually and dramatically, though, the video suggests a different framing. We see Warren’s three brothers, who appear darker than she is. It seems that we might be seeing them not only because they are Republicans, as they say, but also because they look more like what we imagine Native Americans should look like. A female cousin is identified as a citizen of the Cherokee Nation. And the centerpiece of the clip is the DNA-test reveal: the professor confirms that the senator has Native American blood.

Within hours of the appearance of the video, Kim TallBear, a professor at the University of Alberta and a leading expert on the use of DNA testing in tribal communities, posted a statement. Sharply critical of Warren’s behavior and publicity surrounding the test, she pointed out that tribal governments have developed an approach for determining who belongs to a tribe that is explicitly not based on the results of DNA tests. Still, she wrote, Warren and her staff “know very well that the broader US public will understand a DNA test to be a true indication of Elizabeth Warren’s right to claim Native American identity in some way.”

Just what’s wrong with that assumption is laid out in an essay published on ThinkProgress last year by the indigenous activist Rebecca Nagle: Warren, Nagle wrote, is positioning herself as a representative of people whose experience she does not share or understand. Warren has been criticized for failing to meet with Native American leaders, and she has garnered no praise from them for her legislative work (though she has recently signed on to several bills that address indigenous issues). Her visibility as an ostensible Native American exacerbates the invisibility of people who have grown up and live as Native Americans. “As contemporary Native Americans, we live in the space between Donald Trump and Elizabeth Warren, between the stereotypes that were created to excuse the wholesale slaughter of our people and the stereotypes that were created to excuse the wholesale appropriation of our identity and cultures,” Nagle wrote. “The Trumps and Warrens of the world leave very little space for us to exist—which, when you understand the history of the United States, makes perfect sense.”

Warren ended up providing one of the clearest examples yet of how Trumpian rhetoric shifts the political conversation. The woman who is hoping to become the most progressive Democratic nominee in generations is not merely letting herself get jerked around by a Trumpian taunt. She is also reinforcing one of the most insidious ways in which Americans talk about race: as though it were a measurable biological category, one that, in some cases, can be determined by a single drop of blood. Genetic-test evidence is circular: if everyone who claims to be X has a particular genetic marker, then everyone with the marker is likely to be X. This would be flawed reasoning in any area, but what makes it bad science is that it reinforces the belief in the existence of X—in this case, race as a biological category. Warren’s video will hardly convince a Trump voter, who will see only a woman who feels that she has to prove something. Trump himself has already walked back his promise of a million-dollar charity donation. Warren, meanwhile, has allowed herself to be dragged into a conversation based on an outdated, harmful concept of racial blood—one that promotes the pernicious idea of biological differences among people—and she has pulled her supporters right along with her.