U.S. Rep. Diana DeGette — the dean of Colorado’s congressional delegation — conceded defeat in the race for the 1st Congressional District a day after losing to Democrat rival Melat Kiros in their party’s primary contest.

“I want to congratulate Melat Kiros for her victory last night, and I want to wish her all the best in her future,” DeGette said in a statement.

“Frankly, this was not the way I would have wanted to end my career in politics, but I’m proud of my accomplishments from protecting the environment and cleaning up toxic waste to jumpstarting research that will cure previously deadly diseases to fighting for reproductive rights,” said DeGette, who is serving her 15th term in Congress. “I strive every day to be the quintessential legislator, passing bills of my own design and collaborating with colleagues on both sides of the aisle to make a better society for all Americans. Sadly, in our toxic political climate, there seems to be little room for that type of politician anymore.”

DeGette thanked her supporters, as well as the staffers for her campaign and congressional office.

In the equivalent of a political earthquake, Kiros, a 29-year-old Democratic socialist, defeated DeGette. The Associated Press called the race at 10:03 p.m., with Kiros leading DeGette by just under 6 points with 78% of the vote counted.

In a speech before supporters, Kiros framed her victory as part of a larger movement within her party.

“From coast to coast, we are taking back our party,” she said.

“Denver voters of all ages of all races and all religions sent a clear message, we will not wait. We will not wait to take the fight to Donald Trump. We will not wait to abolish ICE and pass Medicare for all,” she said. “We will not wait to end the genocide.”

DeGette, a former state lawmaker and civil rights lawyer who was first elected to the district in 1996, had faced the toughest reelection challenge of her career as Kiros, a political newcomer and first-time candidate, sought to capitalize on upsets scored by fellow socialists across the country in recent weeks.

Kiros, a former corporate attorney who immigrated from Ethiopia to the United States with her parents as an infant, announced her candidacy last year.

At her election watch party, the crowd, mostly millennials and Gen Zers, swelled as the results rolled in. Many sported pins, shirts and hats supporting the Democratic Socialists of America. A prominent internet personality, Hasan Piker, was in attendance.

The heavily Democratic seat, which nearly coincides with Denver’s footprint, hasn’t sent a Republican to Congress since 1970. In the decades since, it’s been represented by just two lawmakers, Democrats Pat Schroeder and DeGette, marking the longest stretch in the country’s history that any congressional district has been represented by women.

That won’t change after this year’s election, though a DeGette loss would also go down in the books. In the last 50 years, only one House incumbent has lost a bid for reelection in a Colorado primary, in 2020, when Republican Lauren Boebert unseated five-term U.S. Rep. Scott Tipton in the 3rd Congressional District.

Although Kiros landed top-line designation on the primary ballot at the Democrats’ district assembly in April — coming within a handful of delegate votes of keeping the incumbent off the ballot — DeGette’s allies began sounding the alarm earlier this month when internal polling reportedly showed DeGette leading Kiros within the margin of error.

In the weeks since ballots went out, outside groups have poured millions into advertising, mostly attacking Kiros by trying to tie her to some of DSA’s more unusual positions, including abolishing the U.S. Senate, pulling the United States out of NATO and essentially abolishing law enforcement.

Kiros said earlier this month at a candidate forum sponsored by Colorado Politics and the Denver Press Club that she didn’t agree with those provisions in the recently adopted DSA platform but said her campaign was focused on fighting for working people, making Denver more affordable and battling government corruption.

While she hasn’t enjoyed the level of outside spending that’s buoyed DeGette, Kiros has benefited from a surge of DSA enthusiasm after its aligned candidates defeated two House Democrats in last week’s New York primaries.

Her supporters said volunteers from around the country completed hundreds of thousands of calls over the weekend before the primary, urging Denver voters to return their ballots.

DeGette, for her part, notes that she’s poised to take the gavel of an important subcommittee on public health policy in the next Congress, if Democrats win the majority in the House, as polling suggests is likely.

Reporter Nicholas Fogleman contributed to this article.