U.S. Senator Elizabeth Warren took the first step toward a 2020 presidential run on Monday, becoming the most prominent Democrat to announce a challenge to Republican President Donald Trump.

Warren, a liberal firebrand from Massachusetts who has frequently clashed with Trump, said she had formed an exploratory committee, which will allow her to begin raising money as part of what is expected to be a crowded Democratic field before the 2020 presidential election.

Trump, who had promised $1 million to her favorite charity if she took a DNA test that showed she had Native American blood, greeted the results with a shrug, saying, “Who cares?”

Warren said in September she would take a “hard look” at running for the Democratic nomination to challenge Republican Trump in 2020. The former Harvard Law School professor campaigned with Democratic presidential candidate Hillary Clinton in 2016 and attacked Trump as an “insecure money grubber” driven by greed and hate.

Trump has cast aspersions on Warren’s claim to Native American ancestry, referring to her as “Pocahontas.”In October, Warren released a DNA analysis she said supported her assertion that she had Native American lineage that goes back six to 10 generations.

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 some Native American groups while others criticized Warren for trying to lay claim to a tribal nation.

Warren, an architect of the Consumer Financial Protection Bureau set up after the 2008 financial crisis, has been a strong voice in the U.S. Senate on financial issues and a self-described defender of the ordinary American against powerful interests.

“Elizabeth grew up on the ragged edge of the middle class in Oklahoma and became a teacher, a law professor, and a U.S. Senator because America invested in kids like her,” it says.