“Members are looking over their shoulders,” said Rep. John Yarmuth (D-Ky.), chairman of the Budget Committee.

The list of Democrats facing primaries is growing as the restive liberal base fights hand to hand in skirmishes across the map. A New York district attorney race erupted onto the national scene last month, with the result between a progressive insurgent and the establishment Democrat still up in the air.

Meanwhile, liberals see the vulnerability of more established candidates at the top of ticket, as former Vice President Joe Biden’s presidential bid has hit a significant speed bump, while diverse and more liberal candidates, such as Sens. Kamala Harris of California and Elizabeth Warren of Massachusetts rise in the polls.

There are still questions about how far-reaching and organized the effort to remake the Democratic Caucus in the House will be — and whether it could jeopardize the party’s control of the chamber. But the uptick of actual and threatened primary challenges presents an additional headache for the party as it seeks to hang on to its majority next year. An Associated Press analysis found that 40 percent of currently declared Democratic challengers were in districts with sitting Democrats.

Immediately after the 2018 elections, the progressive group Justice Democrats put incumbents on notice, vowing to focus on sitting Democrats. Six months later, it’s announced only two recruits. The targets: seven-term Rep. Henry Cuellar of Texas and 16-term Rep. Eliot Engel of New York.

Despite initially endorsing Justice Democrats’ modus operandi of targeting Democrats, joining a launch call with them in November, Ocasio-Cortez is staying on the sidelines — for now.

“I haven’t looked into either of these races, so I need to take a look at it,” Ocasio-Cortez, who rocketed onto the national scene after defeating then-House Democratic Chairman Joe Crowley, told POLITICO last month.

“But frankly, votes like [the border aid bill] certainly grind my gears,” she added, delivering a veiled threat to her colleagues.

Though Ocasio-Cortez has decided to remain mum on Justice Democrats’ new recruits, her chief of staff is not — and members have taken notice.

Hours after Ocasio-Cortez told reporters she needed to take a closer look at the race before deciding whether to get involved, her chief of staff, Saikat Chakrabarti, tweeted support for Cuellar’s challenger, immigration rights attorney Jessica Cisneros.

“Cuellar says he knows Texas. When I lived in TX, I don’t recall people wanting their reps to be bought out by big corps,” Chakrabarti wrote, directing followers to donate to Cisneros.

Chakrabarti’s tweet irked some members.

“If my chief of staff endorsed a primary challenge without my direction,” Yarmuth said, “they wouldn’t be my chief of staff anymore.”

In an effort to hamstring primary challengers, the Democratic Congressional Campaign Committee fired a warning shot to the party’s consultants in March, telling them they risked losing the party committee’s business if they worked for anyone challenging a sitting member of Congress.

“The question that comes up all the time is, is there anybody internally assisting and abetting, encouraging people to run against incumbents?” Rep. Bill Pascrell (D-N.J.), who has faced Democratic opponents in previous cycles, said of members and their staffers.

But the DCCC’s so-called blacklist has only inflamed tensions more. The left is trying to build an alternative consulting infrastructure to support these insurgent candidates. Two alumni of Bernie Sanders’ 2016 presidential campaign rolled out plans for a new firm last week, the Daily Beast reported.

In addition to Cuellar and Engel, a number of other Democratic incumbents are facing the possibility of strenuous primary challenges, including four House Democrats from New York, and Reps. Diana DeGette of Colorado and David Scott of Georgia, and Massachusetts Sen. Ed Markey.

The 2020 election cycle would hardly be the first in which rebels in either party took aim at the establishment. Typically, they have little success: In 2018, just four House incumbents were defeated in primaries, two Democrats and two Republicans.

Justice Democrats hopes to be a galvanizing force to change that. The group plans to back opponents to sitting Democrats who don’t support progressive ideals or who failed to use their position as lawmakers in more aggressive forms, the group says.

Though promising to dedicate more attention to Democrats, the group is also open to getting involved in a small number districts that could be turned from red to blue, according to Executive Director Alexandra Rojas.

Justice Democrats is eyeing challenges to Reps. Frank Pallone (D-N.J.), Stephen Lynch (D-Mass.) and Don Beyer (D-Va.), according to a source close to the group.

Rojas didn’t deny or confirm any of the names, saying, “Anywhere we haven’t announced yet means that we may or may not have someone.”

Though members have expressed frustration and concern about primary challenges, there appears to be less fear among members about the power of Justice Democrats, which has struggled to fundraise and provide a clear picture about where it plans to invest its time.

The recent district attorney race in Queens highlighted the growing party divide, as New York lawmakers Gregory Meeks and House Democratic Caucus Chairman Hakeem Jeffries threw their weight behind the establishment candidate, Melinda Katz, the borough president. In a statement, days from the primary, Meeks blasted Sanders and Warren for getting involved in the local race on behalf of the insurgent candidate.

The episode rankled progressive activists such as Shaun King, a Sanders supporter, who backed outsider candidate Tiffany Cabán.

“Meeks should absolutely be challenged and defeated for his seat in Congress,” said King, co-founder of the Real Justice PAC.

King then directed his ire toward Jeffries, who he said is “out of step” with the progressive base. King took issue with Jeffries’ support of Katz, the establishment-aligned candidate who is ahead by only 20 votes, with the count still ongoing.

“Jeffries continues to duck and dodge on impeachment, continues to fail to support ‘Medicare For All,’ and seems more interested in rising up the ranks of power than actually taking bold stands for his constituents,” King said, adding that he thinks the caucus chairman, who is on a leadership fast-track, should be challenged in a primary “without hesitation.”

“The leadership of Congressman Hakeem Jeffries on criminal justice reform issues, including the dismantling of ‘stop-and-frisk’ in NYC, ending inmate-based gerrymandering in the state, electing former District Attorney Ken Thompson in Brooklyn and the recent passage of the Historic FIRST STEP act speaks for itself,” Jeffries spokesman Michael Hardaway said. “If you don’t know, now you know.”

Asked whether she agreed with King’s call for a primary challenge against Meeks and Jeffries, Rojas dodged. “Every politician needs to be on notice,” she said.

But six months after POLITICO reported that Justice Democrats was weighing a potential challenge to Jeffries according to two sources with direct knowledge, the group has not produced a candidate against him or Meeks or any other New York lawmaker aside from Engel.

King “came into my district and tried to hold a rally and only eight people showed up,” Meeks said. “Come on after me. You think you can get me? Come on.

“I’m preparing; I know Hakeem is,” Meeks continued. “And if somebody decides to run, we’re ready. But you’re not going to catch us by surprise.”