Updated at 8:41 a.m. ET
Cori Bush, a nurse and Black Lives Matter activist, has ousted longtime Missouri U.S. Rep. William Lacy Clay in a Democratic primary, according to The Associated Press.
It's the latest example of a progressive challenger topping a long-tenured Democratic incumbent.
"It is historic that this year, of all years, we're sending a Black, working-class single mother, who has been fighting for Black lives since Ferguson, all the way to the halls of Congress," she said in her victory speech.
Clay, who's also Black, has represented the state's 1st Congressional District, around St. Louis, since 2001. He succeeded his father in representing the district.
The younger Clay topped Bush by 20 percentage points in the 2018 primary, but Bush's profile has risen since then, partly because of a documentary that also profiled New York Rep. Alexandria Ocasio-Cortez.
Bush raised $562,309 for this year's primary challenge — not too far behind the $740,525 Clay raised.
Bush was endorsed by Vermont Sen. Bernie Sanders; Justice Democrats, a group closely aligned with Ocasio-Cortez; and Jamaal Bowman, who dispatched with longtime New York Democratic Rep. Eliot Engel earlier this summer.
Clay's backers, including fellow members of the Congressional Black Caucus, maintain he's "no moderate Democrat," citing, for instance, his support of "Medicare for All."
"This is a huge upset and another groundbreaking win for our movement against a corporate-backed political dynasty," Alexandra Rojas, executive director of Justice Democrats, said in a statement late Tuesday.
The district is very liberal, so it's likely Bush will win November's general election. In 2018, Clay topped a Republican challenger by 63 percentage points.
If elected, Bush would become the state's first Black woman in Congress, according to St. Louis Public Radio.