(Bloomberg)—The atmosphere at Buunni Coffee in the Bronx is thick with the aroma of roasted Ethiopian beans and anti-establishment fervor.

The shop is in the Riverdale neighborhood represented for more than 30 years in the House by Democrat Eliot Engel, a close ally of Speaker Nancy Pelosi. Wielding their personal laptops and cell phones, a crew of volunteers mostly in their 20s and 30s is trying to change that.

“Hello, I’m calling on behalf of Jamaal Bowman,” begin most calls from a make-shift phone bank upstairs, introducing a progressive candidate few people in the district have ever heard of. A lot of the connections end abruptly. But occasionally, interest is piqued, and another potential voter’s name is logged for the middle school principal endorsed by Justice Democrats, the progressive activist group that backed Alexandria Ocasio-Cortez in a neighboring district.

The group is hoping to repeat Ocasio-Cortez’s stunning 2018 Democratic primary victory over Joe Crowley, who was a member of House leadership and a 20-year incumbent. Energized by that upset, the Justice Democrats who has endorsed candidates in Massachusetts, Texas and Ohio to challenge Democratic incumbents they deem as too moderate to reflect the progressive energy animating voters in solidly blue districts.

It’s a major 2020 headache for Pelosi. She often reminds her caucus that their House majority depends on defending and flipping swing districts where middle-of-the-road voters are turned off by progressive causes like Medicare for All and the Green New Deal.

Losing her incumbents to upstart challengers risks ceding crucial seats to Republicans and playing into President Donald Trump’s attempt to present Ocasio-Cortez and her closest allies—Ayanna Pressley of Massachusetts, Rashida Tlaib of Michigan and Ilhan Omar of Minnesota—as the face of a Democratic Party trending towards socialism.

Bowman, 43, an education-reform activist from Yonkers, is one of Engel’s two leading primary challengers. Another is educator Andom Ghebreghiorgis, 33, of Mount Vernon. But it was Bowman who won the endorsement of Justice Democrats, a progressive badge of honor also sought by Ghebreghiorgis and about 10 others vying for the Democratic nomination in New York’s 16th Congressional District.

The district is heavily Democratic and Engel, 72, has been entrenched. He handily defeated three Democratic primary challengers in 2018 with 74 percent of the vote—and didn’t even have a Republican opponent in the general election.

But for Bowman and other progressives, too many Democrats in such safe districts haven’t changed with the times and don’t reflect the more leftward tilt of their constituents.

“A corporate Democrat and a paper progressive,” is how Bowman dismissively described Engel.

The fight for Engel’s seat is but one of the tests for whether Ocasio-Cortez’s surprise 2018 victory was a template for efforts to yank the party further left, which aren’t limited to Justice Democrats.

Engel’s fellow New Yorkers such as House Judiciary Chairman Jerrold Nadler, Carolyn Maloney, Nita Lowey, Kathleen Rice, and Yvette Clark, are among those facing primary challenges, as are Ways and Means Chairman Richard Neal of Massachusetts, Henry Cuellar in Texas and Minority Leader Steny Hoyer of Maryland.

Engel said he wouldn’t know Bowman “if I fell into him” and expressed confidence he won’t lose the primary—to anyone.

He concedes that Justice Democrats “did catch lightning in a bottle” by backing the rise of Ocasio-Cortez in 2018. But he suggests the group is seriously miscalculating by “going around the country thinking they can catch lighting in a bottle again in many other places.”

Justice Democrats, which was founded by former staff members of the Bernie Sanders 2016 presidential campaign, is trying to do just that.

Along with Bowman, the organization so far this year has endorsed Jessica Cisneros to challenge Cuellar in Texas; Holyoke Mayor Alex Morse in his Massachusetts primary bid against Neal; and Morgan Harper in an Ohio challenge to Representative Joyce Beatty. The group has also endorsed Marie Newman, who lost her 2018 challenge to Representatives Dan Lipinski in Illinois and is running against him again, and Cori Bush, who lost to William Lacy Clay in Missouri and is running against him again. Progressive Betsy Sweet has the group’s backing in the primary vying to defeat Republican Senator Susan Collins, as well as Kara Eastman in her bid to unseat Nebraska Representative Don Bacon.

The Justice Democrats’ website plays up its ties with Ocasio-Cortez and the rest of the squad, but the four freshmen aren’t now openly or actively campaigning against their House colleagues. One page sells t-shirts, hoodies and tank tops touting “Ayanna & Ilhan & Rashida & Alexandria” and “Green New Deal.”

“We thought Jamaal had the best shot to take on someone who is difficult to beat,” said Justice Democrat spokesman Waleed Shahid. He pointed to Bowman’s background founding the Cornerstone Academy for Social Action, and his advocacy for equitable school funding and opposition to standardized school testing.

Shahid said the group’s assistance for Bowman is similar to how it is operating for other insurgent House campaigns—aiding in his launch, helping find staff and making voter contacts. Justice Democrats will use its “pretty wide net” of small-donation contributors to provide support, he said.

Bowman and Ghebreghiorgis acknowledge they have a steep, uphill battle to unseat Engel.

Ghebreghiorgis said eventually one of them should drop out to prevent a split of the progressive vote.

Both seize on election data reflecting that only about 7% of the district’s registered voters showed up to cast ballots in the 2018 Democratic primary, and the Bronx portion of district—which stretches to southern Westchester County—is under-represented in the turnout.

They say that suggests voters aren’t engaged by Engel and that there’s a lot untapped votes that could be won by a challenger.

“It tends to make you think there’s actually a capacity to mobilize and bring people into the fold in the Bronx, who have historically not been voting,” Ghebreghiorgis said.

Out on the stump, Bowman touts what is becoming a familiar progressive agenda. He is for Medicare for All, free public college tuition, overhauling the criminal justice system and the Green New Deal.

“My opponent voted for an unjust war in Iraq, deregulating Wall Street, school privatization and building more prisons,” Bowman said in his launch video. “While the very few at the top continue to build their wealth and power, the majority of us continue to struggle.”

At a picnic by the grassroots “Indivisible” group that began in opposition to Trump’s 2016 election, Engel made a point to highlight that he has joined the call for an impeachment inquiry, which now roughly half of the 235 House Democrats want to pursue.

The incumbent congressman does have some progressive bona fides and a record of liberal achievements. Kenneth Jenkins, the Westchester deputy county executive, and former president of the Yonkers branch of the NAACP, said he’s been an Engel supporter for years, dating from their work together on desegregation and housing issues.

“People forget that Eliot was the rabble-rouser of his time,” Jenkins said. “He was the renegade and the liberal.”

When Engel first ran for the state Assembly in a 1977 special election, he was the insurgent liberal nominee who defeated both the Democratic and Republican candidates. And in his first race for a U.S. House seat, in 1988, he beat a 10-term congressman, Mario Biaggi, who had already resigned his seat after being convicted on racketeering charges, but remained on the primary ballot.

At Buunni Coffee, some of the volunteers said they hadn’t met Bowman yet. But nearly all were aware he’d gotten the backing of Justice Democrats, the group famous for backing Ocasio-Cortez’s 2018 candidacy.

Jatnna De La Cruz, 20, a City College of New York political science student, said that “overlap with the Justice Democrats and AOC” played some role in her wanting to canvass for Bowman, but it was not the only reason.

Asked what she knew about Engel, she said, “I know is he has been in Congress for 30 years.”

When Bowman himself arrived, he was clearly happy to find such a crew of canvassers. He said he’s proud of his endorsement from the Justice Democrats: “It comes up and I bring it up, I mention it because I want people to know our ideology and where we are coming up.”

He also recognizes a campaign to topple an incumbent won’t be built overnight.

“It’s still early,” Bowman said. “We’re just working. We have our heads down. We’re grinding.”