WASHINGTON (Reuters) - Democratic Senator Elizabeth Warren, ridiculed by U.S. President Donald Trump as “Pocahontas” for claiming Native American heritage, hit back on Monday with DNA evidence she said supported her assertion, a possible preview of a bare-knuckles presidential campaign in 2020.

The Massachusetts lawmaker, known as a liberal firebrand in her party, said last month she would take a “hard look” at running for the Democratic nomination to challenge Republican Trump in 2020. She and Trump clashed frequently through the 2016 presidential campaign and Trump has cast aspersions on her claim to Native American ancestry.

“When I decided to run for Senate in 2012, I never thought that my family’s Native American heritage would come under attack and my dead parents would be called liars,” she said in a statement on Monday.

“And I never expected the president of the United States to use my family’s story as a racist political joke,” she said.

Trump taunted Warren over the issue at a July rally in Montana.

“I will give you a million dollars to your favorite charity, paid for by Trump, if you take the test and it shows you’re an Indian,” he said. “I have a feeling she will say ‘no.’”

Warren reminded the president on Monday of his promise. “Please send the check to the National Indigenous Women’s Resource Center,” she said on Twitter.

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When asked about the DNA test, Trump said: “Who cares?” Then he denied making the comment, as he left Washington to visit hurricane-stricken areas in Florida and Georgia.

Later, Trump suggested to reporters in Georgia he could pay the $1 million he had wagered, but with a caveat: “I’ll only do it if I can test her personally. That will not be something I will enjoy doing either,” he said.

Trump’s use of the name Pocahontas refers to a 17th century Native American woman associated with the British colony in Jamestown, Virginia, and was aimed at drawing attention to a controversy over her heritage raised during Warren’s 2012 Senate race. Trump’s mocking reference has drawn criticism from Native American groups.

POSSIBLE PRESIDENTIAL RUN?

Warren provided the DNA test results in a statement, showing the lineage goes back six to 10 generations. bit.ly/2OqLmUz

The analysis of Warren’s DNA was done by Carlos Bustamante, a Stanford University professor whom the Boston Globe reported was an expert in the field.

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The professor concluded that most of the senator’s DNA showed European ancestry but that it had a Native American segment. Warren has said that her Native American ancestry possibly goes back to the 1700s, including Cherokee blood on her mother’s side, according to family lore.

Warren’s release of the results was criticized by Cherokee Nation Secretary of State Chuck Hoskin Jr., who said; “Using a DNA test to lay claim to any connection to the Cherokee Nation or any tribal nation, even vaguely, is inappropriate and wrong.”

Warren’s move could be a prelude to a possible presidential run.

An architect of the Consumer Financial Protection Bureau set up after the 2008 financial crisis, Warren has been a strong voice in the U.S. Senate on financial issues.

Warren, campaigning with Democratic presidential candidate Hillary Clinton in 2016, attacked Trump as an “insecure money grubber” driven by greed and hate.

“I hope she’s running for president, because I think she’ll be very easy,” Trump said as he left the White House on Monday.