The grassroots left scored one of its biggest primary victories of the year Tuesday, as Ayanna Pressley took down 10-term U.S. Rep. Mike Capuano in Massachusetts. On Thursday, progressives have a chance at an even bigger win in Delaware, where Kerri Evelyn Harris is hoping to hand centrist Democratic Sen. Tom Carper his first electoral defeat of his 40-year political career.

Harris, a veteran and community activist, has never before run for office and is a clear underdog against Carper, a 71-year-old, three-term senator who has also served as governor, congressman, and state treasurer since first being elected to statewide office in 1976. But an upset no longer seems out of the question after Pressley’s shocking victory, which came a little more than two months after Alexandria Ocasio-Cortez stunned Rep. Joe Crowley, also a 10-term incumbent. Yes, Carper is a sitting senator, not a sitting congressman. But Delaware is tiny enough that it has only one at-large representative in the U.S. House, and so a Senate primary in the state and a House primary face the same electorate.

Like Pressley and Ocasio-Cortez, the 38-year-old Harris has paired a progressive policy agenda with a lived-experience argument in a bid to unseat an older white man who has been a fixture in national politics since the turn of the century. “I’m running because I know what you’re experiencing right now,” Harris told a debate audience last week. “And I know that a firm handshake, a kind smile, a witty remark, is not enough to move us forward. We’re suffering.”

Like Capuano, Carper has put a premium on his political résumé and deep ties to the community. Unlike Capuano, Carper is a moderate and would have been vulnerable to a challenge from the left even if the question of identity and representation were absent from this one. He has the backing of his party’s establishment—including an endorsement from former Vice President and Delaware Sen. Joe Biden—as well as from mainstream environmental and labor groups. But the activist left’s case against him looks something like this: He voted to authorize the invasion of Iraq, opposes Medicare for All, has backed offshore drilling, and he was one of about a dozen Senate Democrats who helped loosen key provisions of the post-financial crisis banking rules known as Dodd-Frank—the latest example of him siding with the banking industry that is responsible for roughly one in every 10 jobs in the state and which has donated millions to Carper.

Harris, meanwhile, has shrugged off the progressive label—“I avoid that term because it’s shut some people off to it,” she told Vox recently—but her policy positions make clear she is one. She supports Medicare for All, a $15 minimum wage, a Green New Deal, the abolishment of the U.S. Immigrations and Customs Enforcement agency, legalizing marijuana, ending mass incarceration, and eliminating all student debt. Like Ocasio-Cortez and Pressley, Harris has also sworn off corporate PAC money. All of that was enough to earn her Ocasio-Cortez’s stamp of approval: The New York congresswoman-to-be has endorsed Harris, lent her campaign staff, and travelled to Delaware last week to stump for her. And like a number of other political newcomers this cycle, Harris would make history if elected this November: She would become the first woman, first person of color, and first openly LGBTQ person sent to the U.S. Senate by Delaware voters.

Polling has been spotty—Carper led by 30-plus points at the end of July, the last time Gravis surveyed the state—but the fundraising numbers make Carper’s advantage clear. As of mid-August, he had raised $3.5 million and spent $3.3 million; Harris had raised roughly $114,000 and spent $63,000. By any traditional measure, then, Carper should be expected to coast to the nomination. But, of course, so too were Crowley and Capuano.