WASHINGTON (AP) — Rep. Henry Cuellar is an increasingly rare politician in the Democratic Party, a conservative-leaning lawmaker whose unapologetic defense of gun rights and the energy industry during his 17 years in Congress long delighted his Texas constituents.

That was once a winning strategy for Democrats running in moderate swaths of the country. But for Cuellar, whose district stretches from the San Antonio suburbs to the Mexican border, those stances could leave him vulnerable to a challenge from the left by 28-year-old immigration attorney Jessica Cisneros. She nearly beat Cuellar in the 2020 primary and is seeking a rematch with hopes of tapping into growing frustration among progressives about the pace of change in Washington.

An FBI search near Cuellar’s home this week could add a new dimension to the contest. Cuellar hasn’t been charged with a crime and the bureau has said nothing about the scope of its investigation, including whether he is the subject of a probe.

But the development added to the stakes of the March 1 primary in Texas, which will usher in several months of contests across the nation to determine which candidates advance to the fall general election. Progressives are closely watching the race as a test of whether they can topple other moderate, establishment-oriented candidates as the primary season unfolds.

“I think Jessica had a strong shot before the investigation,” said Waleed Shahid, a spokesman for the progressive group Justice Democrats, which has backed Democratic primary challengers against more moderate members of Congress around the country. “I think she can win.”

Representatives for Cuellar did not comment for this story. His office issued a brief statement after the search, saying the congressman “will fully cooperate in any investigation.”

“He is committed to ensuring that justice and the law are upheld,” the statement read.

Shahid compared Cisneros to progressive stars like Reps. Alexandria Ocasio-Cortez of New York and Ayanna Pressley of Massachusetts who “have really become rising figures in the party and part of this new generation of leadership.”

When Ocasio-Cortez defeated Joe Crowley in a 2018 primary, she ushered in a new era in which progressives take on veteran, establishment-oriented incumbents in an effort to move the party to the left on issues including the environment and health care.

Progressives hoping to add Cuellar to the list of defeated incumbents are gauging whether the FBI search is the type of late-stage development that could shift the campaign in their favor.

Cisneros has so far not rushed to promote the raid as a potential political liability, saying in a statement only that, “We are closely watching as this develops. In the meantime, we are focused on our campaign.”

Justice Democrats has not showed such restraint, with its executive director, Alexandra Rojas, releasing a statement on Cuellar asking “What is he hiding?” Shahid said Democratic elders have closed ranks around Cuellar, noting that the Texan tweeted that House Majority Leader Steny Hoyer had endorsed him just before word of the FBI search broke.

“In all of our races the Democratic Party establishment tends to consolidate around the incumbent,” Shahid said.

Justice Democrats first recruited Cisneros to run against Cuellar in 2020, after supporting Ocasio Cortez’s upset primary win two years earlier.

Cisneros, who was an intern in Cuellar’s Washington office in 2014, racked up endorsements from many of the left’s leading national voices, including Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts, as well as Ocasio Cortez. She branded Cuellar as “Trump’s favorite Democrat” and ultimately came within 4 percentage points of beating him.

First elected to Congress in 2004, Cuellar serves on the powerful House Appropriations Committee and was outspoken in blaming national Democrats’ move to the left during the 2020 campaign on issues like health care and the environment as contributing to some disappointing losses in the House .

He argued that GOP suggestions that Democrats opposed police, embraced socialized medicine and would sacrifice jobs in key industries like oil and gas created a narrative that helped ensure Democrats retained their majority in the chamber by only the slimmest of margins — even as the more moderate Joe Biden won the presidency.

Cuellar has drawn progressive criticism for years, in part because of the praise he’s attracted from groups like the National Rifle Association. He also was the lone House Democrat to oppose major abortion rights legislation in September. And Cuellar joined a group of moderates who helped force passage of a major public works bill that had broader bipartisan support before Congress could tackle a larger, spending and social welfare package championed by Biden and top progressives. It still hasn’t passed.

The primary’s outcome could prove even more critical this cycle, as Democrats look to defend their narrow control of the House in November.

After topping Cisneros the first time, Cuellar cruised to a nearly 20-point win over a little-known Republican opponent. New congressional maps based on the 2020 census make the district slightly more Democratic, picking up blue territory along its northern extremes near San Antonio.

Still, Republicans are hoping to stay competitive in a district that’s nearly 80% Hispanic, betting they can capitalize on former President Donald Trump’s unexpectedly strong 2020 showing among Latino voters, especially in south Texas. Biden won Latinos by a 59% to 38% margin over Trump two years ago, but that was 7 percentage points lower than Hillary Clinton’s 66% to 28% margin in 2016, according to Pew Research Center data.

Tania Unzueta, political director of the progressive Latino organization Mijente, which has endorsed Cisneros, said the group sees political investment in south Texas as especially important to counter the rise of right-wing candidates and ideology in the area.

“What’s great about it happening close to elections is that people are actually able to take action pretty immediately,” Unzueta said of the FBI search near Cuellar’s home. “And we have a good alternative.”

But Democratic strategist Matt Angle noted that so much remains unclear about the circumstances of the FBI’s investigation and, with more than a month until the primary, the political implications for Cuellar are uncertain.

“That was a contested and competitive primary no matter what,” he said.