The problem I have with “identity politics” is that it’s a phrase mostly used by people who don’t name their identities, against those who do. We all have identities, after all, and in racialised societies like this one it’s ethnic minorities who are guilty of playing “identity politics” for having the audacity to own, articulate or organise around that experience. Meanwhile the majority, who have the luxury of regarding their identities as normal, neutral and invisible, have always mobilised politically around class, region, and whiteness. But that’s not identity politics, that’s just politics, right?

Donald Trump rains insults on Elizabeth Warren after DNA test Read more

All politics are identity politics and, if we really want to use the term, the rightwing purveyors of nativist populism have been among the most devoted practitioners. Remember Margaret Thatcher, invoking Churchillian nativism over the Falkland Islands, whose population, “like the people of the United Kingdom, are an island race”. There is nothing at the moment to suggest the next US presidential election will be between anything other than two white candidates, but that won’t stop Donald Trump from using racist slurs. Because the first campaign video has just landed – with the midterm elections not yet even out of the way – and it’s all about race and identity.

Enter Elizabeth Warren. You may not be that familiar with her yet, but you will be. Or you might know her better as “Pocahontas”, or even “fake Pocahontas” – the name the president uses to mock her claim of Native American heritage. It is, in the darkly effective attention-seeking that is his way, an insult that somehow manages to say Warren has no legitimate claim to be Native American, while simultaneously insulting those who do.

Warren is not really saying she is Native American. That ethnic status has specific meaning in the US, where membership is a question of meeting requirements for tribal citizenship rather than simply proving lineage. But Warren is – as she says – simply telling a story about her family’s identity.

And until recently, she had barely been doing that. The Harvard law professor-turned-senator was better known for a string of “caring capitalism”-type measures: better consumer protection, laws, not unlike those proposed by Labour in Britain, that would give workers the power to hold corporations to account.

But by going into her family background, in the inevitably polarising context of an impending election, Warren’s new video performs a few useful tasks simultaneously. It delves into a down-home Oklahoma narrative about an ordinary middle-class family: three older, brothers all of them former military, some of them Republican voters, and her “momma and daddy”, hardworking Americans who married when barely out of their teens. It doesn’t take a strategic genius to see the utility of this for someone who has been a Harvard law professor – which, as we saw in the backlash to Obama, has come to symbolise the “liberal metropolitan elite” identity that populists, so often themselves the very definition of privilege, have successfully weaponised.

The real point of the film, though, is to show up Trump-type bigotry. It reveals the attitude of her father’s family, which she says was “bitterly opposed” to the fact that her mother was part Native American. “That kind of discrimination,” she says, looking at sepia photos of this family from a time when Oklahoma had only recently ceased to be an Indian nation and become a federal state, “was common at the time.”

Play Video 1:06 Elizabeth Warren hits back at Donald Trump by releasing DNA test – video report

There’s an interview with a cousin who is a citizen of the Cherokee nation, and then – in a big reveal – test results that “suggest that you absolutely have a Native American ancestry in your pedigree,” says Carlos Bustamante, a professor of genetics at Stanford, who analysed Warren’s DNA.

This makes uncomfortable watching. First of all, the relationship between race and genetics is dodgy as hell. The more we understand genetics, the less we understand race – scientists have tried and failed to find any real correlation between the physical characteristics that distinguish us in visible terms from the patterns in DNA variations between us. Ancestry companies, whose business is booming, have focused most of their research on people of northern European descent and very little on everyone else, so just how much they can tell us about someone like Warren’s family is up for debate. Race is actually what Warren is saying it is – a societal experience, a cultural heritage, a shared memory.

Which is why it’s disappointing that Warren should have taken the bait. Obama producing his birth certificate didn’t stop the birthers’ claims – seven years later, a quarter of Republicans still believe them. Why should a far less convincing DNA test stop Trump? He’s already – follow this if you can – denying having denied Warren had Native American heritage anyway. Truth has zero role to play here.

Warren hasn’t used her distant ancestry to mislead. She has dealt with it in the slightly confused way that people with mixed heritage – myself included – often have. And the question as to whether she might have been entitled to use this heritage to claim minority status in university and job applications is an interesting one.

What’s surreal about this whole debate is that, in trying to belittle Warren’s Native American heritage, Trump has multiplied its symbolism. “Fake Pocahontas”: it’s utterly consistent with his need to find one-concept devices for delegitimising his opponents. Obama: “Kenyan”; Clinton: “Lock her up.”

It’s hard to think of any other time when politics would have played out quite like this. In this era of cultural candidates and identity politics, there is on one side a politician who has been reduced to taking DNA tests to prove she is “real”, rather than “fake”; and on the other an incumbent who thinks this ludicrous framework is an appropriate one for a discussion about descending from the indigenous – and still oppressed – inhabitants of his land. I have a feeling about which one is going to be accused of playing identity politics, though, and it’s not going to be Trump.

• Afua Hirsch is a Guardian columnist