U.S. Sen. Bernie Sanders on Friday endorsed congressional candidate Melat Kiros, one of two Democrats challenging 15-term U.S. Rep. Diana DeGette in Colorado’s June primary.

Sanders, a Vermont independent who caucuses with the Democrats, called the 29-year-old Kiros “exactly the kind of bold leader we need in Congress” and said he is “excited” to endorse the first-time candidate, who, like Sanders, describes herself as a democratic socialist.

“She has shown she is not afraid to stand up to corrupt special interests like AIPAC and Big Pharma,” Sanders said in a statement.

“Melat was raised in a working-class immigrant household, and she knows that the current political and economic systems are broken and need bold reform,” he added. “That’s why she has refused corporate PAC donations and will be a great ally in fighting for a progressive agenda that addresses the needs of working families.”

The endorsement from one of the country’s most prominent progressives comes as outside groups are pouring more than $1 million into ads attacking Kiros and defending DeGette.

Colorado voters started receiving primary ballots last week and have until June 30 to return them to their county clerks.

DeGette, 68, a former state lawmaker and civil rights attorney, was first elected to represent the state’s most heavily Democratic seat, Denver-based 1st Congressional District, in 1996 and won reelection by wide margins ever since. The district’s voters haven’t sent a Republican to Congress since 1970.

Kiros, whose parents immigrated to the United States from Ethiopia when she was an infant, launched her campaign last summer after losing her job as an associate at a New York securities law firm after she posted a public letter defending critics of Israel’s military action in Gaza and Lebanon. Since returning to Denver, she’s worked part-time as a barista while pursuing a doctorate in public affairs at the University of Colorado-Denver.

Although DeGette has faced multiple primaries over the last decade, Kiros appears to be the first Democratic challenger since the late 1990s in a position to threaten her reelection.

DeGette came within a few dozen delegate votes of failing to qualify for the ballot at the district’s Democratic assembly in late March, where Kiros received roughly twice as much support as the incumbent.

A third candidate, University of Colorado Regent Wanda James, a longtime Democratic strategist and marijuana entrepreneur, is also running in the primary.

Kiros welcomed the endorsement in a statement.

“Bernie Sanders has been right about Medicare for All and getting corporate money out of politics for decades, before it was popular in Washington, before it was safe,” Kiros said. “We need more people in Congress willing to stand up to the wealthy and powerful, even when it costs them something.”

Kiros credited Sanders, who won Colorado’s 2020 presidential primary and carried the state’s Democratic caucuses in 2016, for encouraging Denver residents to engage in politics.

“That movement is real, it’s alive in this race, and I plan to carry that fight to Congress,” she added.

A spokesman for DeGette’s campaign didn’t respond to a request for comment on Sanders’ endorsement.

Kiros has also been endorsed by the Democratic Socialists of America, Justice Democrats and the Sunrise Movement, a group devoted to countering climate change.

DeGette, who chairs the House Reproductive Freedom Caucus and is an original co-sponsor of the Medicare for All Act, has dozens of endorsements, including from the National Organization for Women, Reproductive Freedom for All, the Colorado AFL-CIO, Planned Parenthood Action Fund and the campaign arms of the Congressional Progressive Caucus and the Congressional Hispanic Caucus.