Representative Dan Lipinski is a rare find in Congress these days: an anti-abortion Democrat who voted against the Affordable Care Act.

Of the 34 Democrats who broke with the party on that most consequential vote eight years ago, just three remain in office. And none have had it quite so easy as Lipinski, a low-key former college professor who in 2005 inherited a Chicago-area House seat that his father held for two decades.

He’s escaped any real threat from Republicans; they defeated most of the other anti-Obamacare Democrats but couldn’t compete in his solidly blue district. And the left has been too busy defending the law and fighting other battles in the years since.

But Lipinski, 51, is now facing a serious primary challenge for the first time in a decade, in what progressives say is a long-overdue political reckoning for a congressman whose voting record has gotten too far to the right of his constituents. Illinois’s third congressional district, which includes a portion of Chicago and suburbs to the south and west, went for Bernie Sanders in the 2016 presidential primary and backed Hillary Clinton by 15 points in the general election.

Lipinski’s opponent in the March 20 primary, Marie Newman, has the backing of an array of national progressive organizations, including NARAL Pro-Choice America, EMILY’s List, the Progressive Change Campaign Committee, and the Service Employees International Union. And in an unusual break with Congress’s clubby norms, she’s won endorsements from Senator Kirsten Gillibrand of New York and two of Lipinski’s long-serving Democratic colleagues in the Illinois delegation: Representatives Jan Schakowsky and Luís Gutierrez.

Schakowsky told me that in her 19 years serving in Congress, she’s never endorsed against a sitting House Democrat, much less one in her own state. Lipinski, she said, “has been voting against the Democratic position for such a long time.”

The list of Lipinski’s apostasies goes far beyond Obamacare, Newman supporters say. He’s unequivocally opposed to abortion rights (“I’ve never hidden that,” he told me), voted against recognizing same-sex marriages, and until recently, did not support a path to citizenship for the young undocumented immigrants known as Dreamers who were brought to the U.S. as children. Lipinski has also repeatedly voted against Nancy Pelosi, the House Democratic leader, in the election for speaker.

“He’s just really out of step,” Schakowsky said, “and this is a really progressive moment where new candidates, first-time candidates are running strong—people who are standing up for basic principles that Dan has continually voted against.”

Indeed, Lipinski can thank President Trump for his current political predicament. The same surge of Democratic activism that has prompted a record number of women and first-time candidates to run against Republicans inspired Newman to get in the race against him. “It became clear that nobody was coming to save us,” she told me in a phone interview. “And I stepped up.”

Newman, 53, has never run for office before, but she’s not new to politics. A former advertising executive, she’s campaigned against bullying after the trauma her son suffered in school, and she’s served as a spokeswoman for the Illinois chapter of Moms Demand Action, a gun-control group. Newman told me she studied the district for nearly a year before deciding to run, including commissioning polling that indicated Lipinski could be vulnerable. “For me, his votes on immigration and his votes on health care have been astonishing to me and just demonstrate how out of touch he is with the people in this district,” she said, calling his votes “dangerous.”

It was that kind of preparation that impressed progressive activists, who have long grumbled about Lipinski but never found a challenger they viewed as strong enough to take him out. “We believe in her, and that’s the No. 1 reason,” said Ilyse Hogue, NARAL’s president. “And let’s just be clear: It’s not that we didn’t know he was super bad on our issues and on a lot of the issues we care about prior to this year. But you have to have a credible alternative, and he just really hadn’t to this point.”

Pitched primary battles and ideological purity tests have more recently been the domain of Republicans, who watched as conservatives aligned with the Tea Party ousted a number of their House and Senate incumbents, most notably the House majority leader in 2014, Eric Cantor. Democrats have largely kept their eyes on Republicans, but the advantageous political environment this year has changed the calculus, at least when it comes to Lipinski. “2018 will be a year of opportunity for Democrats and progressives,” the PCCC’s Adam Green told me, “and just as we can make some huge gains in typically purple and red districts, we can clean house in blue districts and ensure that we don’t have someone in there who’s undermining everything from the Affordable Care Act to Wall Street reform to choice.”

The Lipinski-Newman primary also happens to be a relatively risk-free fight for Democrats, since the district is so deeply blue. Republicans didn’t even bother recruiting anyone ahead of the filing deadline, so their nominee is likely to be Arthur Jones, a perennial candidate and Holocaust denier who once led the American Nazi Party and told the Chicago Sun-Times that the slaughter of six million Jews during World War II was “an international extortion racket.” (The Illinois Republican Party has disavowed his candidacy.)

With no public polling as yet, both candidates are claiming an edge in the race. Newman’s campaign released an internal poll giving her a five-point lead, but a survey conducted for Lipinski’s campaign found that she had little name-recognition in the district and that he had an enormous, 36-point advantage. Including a $100,000 loan she gave to her campaign, Newman out-raised Lipinski in the fourth quarter of 2017. But his $1.6 million war chest dwarfs the $236,000 she had on hand at the end of the year.

“We’ve had 36 years of Lipinski-ism,” Newman said in a nod to his family’s history in the district, which she mockingly called “the Lipinski monarchy.” “That’s pretty tough to combat,” she said. Lipinski’s father, Bill, first won the seat in 1982 and cleared the way for him to take it 22 years later by dropping out after the Democratic primary in 2004.

While Newman has the support of national progressive groups and SEIU, Lipinski retains the backing of local mayors and the bulk of the labor movement. “His brand is well-known there,” said Kristen Hawn, a Democratic consultant who works for the campaign arm of the Blue Dog Coalition. Lipinski is a co-chairman of the Blue Dogs, the group of fiscally-conservative Democrats in the House.

Lipinski has made some moves in the direction of the Democratic base, especially on the issue of immigration. While he voted against the Dream Act in 2010, he joined a new bipartisan group called the Problem Solvers Caucus in backing a path to citizenship for recipients of the Deferred Action for Childhood Arrivals program. Like all other Democrats, he’s voted against GOP attempts to repeal Obamacare, and in response to criticism from the left, he reiterated his support for legislation that would gradually increase the federal minimum wage to $15 an hour.

But on the two core issues that separate him from the vast majority of Democrats currently serving in Congress—his vote against the ACA and his opposition to legal abortion—Lipinski hasn’t budged. “I don’t regret my vote,” he told me in a phone interview. “I think what we’ve seen happen with the Affordable Care Act validates that vote. We should have had a better bill.” He cited a lack of cost containment and rising premiums as problems with the law, along with the early failure of the Class Act, a long-term care program that Congress ultimately scrapped. On abortion, Lipinski said he’s been “out front about being pro-life” and called Newman’s position “extreme.”

As for losing the support of Schakowsky and Gutierrez, Lipinski didn’t seem to take offense. He noted that he supported Schakowsky for a House leadership post years ago and that Gutierrez and he had “different styles.” “Luis is much more of a bomb-thrower,” Lipinski said, in a characterization that few in politics would dispute, Gutierrez among them.

Lipinski’s bigger concern was what he called “a Tea Party of the left” in which activists “only want people in the party who agree 100 percent with them.” Eschewing the label of a conservative, he said he was “a common-sense Democrat” and a problem-solver who tried to bring people together.

The Lipinski-Newman primary next month won’t determine the balance of power in Congress, but it can provide an early clue to what kind of Democrat voters want in the age of Trump—the pragmatist or the purist. And it’ll test whether progressive activists muscling up for the fight against Republicans this fall have the strength to take out a conservative Democrat on the way.