They’ve weathered blistering attacks from the president, the exposure of sensitive sources, and the politicization of classified information. And now they’re not getting paid. “I’m not going to try to candy-coat it,” Tom O’Connor, a special agent and president of the FBI Agents Association, told me this week. “We really feel that the financial insecurities we are facing right now equate to a national-security issue.”

On Saturday, the current government shutdown will be the longest in U.S. history—and it could remain shuttered for “months or even years,” President Donald Trump warned Democrats last week. While much of the drama has centered around Trump’s demand for a wall on the southern border, thousands of FBI agents and other federal employees whose unfettered work is crucial to national security have either been furloughed or forced to work with no pay and steep budget cuts.

Morale at the FBI had already been steadily declining for months before the government shut down on December 22, according to current and recently departed agents who spoke to me on the condition of anonymity to discuss their feelings candidly. President Trump’s open warfare on the bureau has made agents’ jobs more difficult, they say, as trust in the FBI wanes among people who identify as Republicans and right-leaning independents. “Part of it is Trump’s constant attacks,” said one agent who left late last year. “Bigger than that, though, is that it seems like a portion of the population believes him. Which makes their jobs harder to do.”

Another agent who left the bureau last year told me that certain leads that might be politically controversial were sometimes tabled indefinitely because they were not seen as worth incurring the wrath of the Trump White House. In the two and a half years since the FBI launched its counterintelligence investigation into potential coordination between members of Trump’s campaign and Russia, the president has chided the FBI, former FBI Director James Comey, Special Counsel Robert Mueller, the Russia “witch hunt,” and the “deep state” in dozens of tweets, rallies, and interviews. Last April, he called the FBI and Justice Department’s desire to withhold sensitive information related to the ongoing investigation “an embarrassment to our country.” The withering morale and possibility of having to work without pay has made it increasingly difficult to recruit new agents, the agents said.

The government shutdown, now heading into its 20th day, is the cherry on top of a galling two years. “You know the old adage that crime doesn’t pay? Well right now, agents are starting to feel like neither does the federal government,” O’Connor said. In a conference call with reporters on Thursday, O’Connor said that nearly 5,000 special agents, intelligence analysts, attorneys, and professional staff are currently furloughed, resulting in reduced staffing for “critical functions that support field operations.” None of them are being paid, he said. He wouldn’t elaborate on which investigations were being impacted, but emphasized that a lack of funding has hurt agents’ ability to do their job “completely and to the fullest ability we have.”

O’Connor also described a mounting backlog at Quantico labs, which provide forensic-analysis support services to the FBI, and said that funds supporting drug trafficking and undercover operations have been dangerously limited. Some, particularly those who work at Quantico labs, are not even allowed to come to work because of the shutdown. “FBI headquarters is trying to make sure that the most important topics are covered,” O’Connor said. “But that will get more and more difficult as the pot of money gets smaller and is not refilled.” According to an FBIAA spokesman, FBI field offices are responsible for allocating their resources and determining which activities are most central to specific missions or operations. Which areas are prioritized—whether it’s drug trafficking, counterterrorism, etc.—is also at the discretion of field-office leadership. “However, as the pool of resources dwindles, the scope of what can be adequately funded will also shrink,” the spokesman, Paul Nathanson, said.

If the issue does not get resolved within the next few weeks, however, agents in various field offices may stage a callout—a coordinated sick day to protest the shutdown. (Transportation Security Administration agents have already begun doing so, according to CNN.) O’Connor said he had not heard of any plans to strike or begin calling in sick en masse, but he emphasized that he would not support it if they did. “Whether we’re paid or not, we’re going to show up and do our jobs to protect the United States,” he said. A coordinated “sick-out” would be one way of protesting the current conditions, since the Taft-Hartley Act, enacted in 1947, prohibits public employees from overtly striking. Federal-employee unions may also find recourse in the courts—some have already filed lawsuits arguing that requiring employees to work without pay violates the Fair Labor Standards Act of 1938.

For now, the FBI Agents Association is simply pressuring elected officials. In a petition sent to the White House, the vice president’s office, House Speaker Nancy Pelosi, Senate Minority Leader Chuck Schumer, and other House and Senate leaders on Thursday, the agents association warned of the effects of the ongoing shutdown on the bureau’s work. “The operations of the FBI require funding,” the petition reads. “As the shutdown continues, Special Agents remain at work for the American people without being paid, and FBI leadership is doing all it can to fund FBI operations with increasingly limited resources—this situation is not sustainable.” Asked what the agents’ next steps will be if the funding is not restored, O’Connor said that they’ll continue to do “the best with what we have.”

“But I think it’s the public that will have an outcry when they see things not being done because we don’t have the funding for it,” he added.

The FBI is not the only agency whose limited budget and resources could compromise national security. More than half of the staff of the newly established Cybersecurity and Infrastructure Security Agency, a division of Homeland Security tasked with protecting the country’s critical infrastructure, have been furloughed, according to DHS. Nearly every employee of the Secret Service—which protects current and former government officials as well as the president—is going without pay, too, according to The New York Times, as are TSA agents and air-traffic controllers. “The growing financial insecurity may lead some agents to consider career options that provide more stability,” O’Connor said on Thursday. “The field is trying to be fully funded and staffed. But as we go forward, that’s going to change.”