Donald Trump has made a habit of questioning people’s origins—particularly those of his political rivals. He spread ”birther” conspiracy theories about Barack Obama, demanding to see the former president’s birth certificate as proof of his American citizenship status. And he has repeatedly called Massachusetts senator Elizabeth Warren a liar for claiming to have Native American heritage. At a rally in Montana this summer, Trump went so far as to make a hypothetical bet. Imagining a debate with Warren, he told the crowd: “I’m going to get one of those little [DNA testing] kits and in the middle of the debate, when she proclaims she’s of Indian heritage… And we will say, ‘I will give you a million dollars, paid for by Trump, to your favorite charity, if you take the test and it shows you’re an Indian.’ Now Warren says Trump needs to pony up. In a highly-publicized ad rolled out today, the Democratic senator revealed the results of a DNA test that provides “strong evidence” she has Native American blood dating back six to 10 generations. She was quick to remind Trump of his pledge: In the video, Warren tells Carlos Bustamante, a professor of genetics at Stanford and adviser to Ancestry and 23andMe: “The president likes to call my mom a liar. What do the facts say?” Bustamante responds, “The facts suggest that you absolutely have a Native American ancestor in your pedigree,” as Warren nods. Bustamante’s full genetic profile of Warren (pdf) is now posted on her website. It’s important to note that DNA ancestry tests are far from perfect science. As the American Society of Human Genetics said in 2010, even comparatively strong genetic databases “reflect a woefully incomplete sampling of human genetic diversity, and this has important consequences for the accuracy of ancestry inference,” and samples from people of Native American descent tend to be particularly lacking. In addition, some Native Americans have expressed concerns over the practice of genetic testing, as The Atlantic reported in 2015—both because of fears that the data might be used for exploitative purposes, and because tribal identity is not just a matter of genetics but one of culture, parentage, and political citizenship. Regardless, as Annie Linskey points out in The Boston Globe, the ad is certainly important in that it is “another indication of how seriously Warren is considering running for president.” Trump and his die-hard supporters seem unlikely to be persuaded that Warren is telling the truth about her heritage. White House counselor Kellyanne Conway sought to dismiss the value of the DNA test, telling reporters, “everybody likes to pick their junk science or sound science depending on the conclusion it seems some days.” And Trump himself told reporters, “Who cares?” But some observers say that convincing Trump was never the point. Whether or not Warren decides to run, she seems to be attempting to avoid the pitfalls that Hillary Clinton faced as the first female Democratic nominee for the presidency. Clinton was criticized for being overly private during her campaign, often chafing at releasing personal information. As Linskey points out, “By taking a DNA test, Warren is showing that if she runs for president, she plans to be a very different candidate than Hillary Clinton was.”