FBI agents have lost irreplaceable sources. Joint Terrorism Task Force officers can’t get into the bureau’s computer systems. Federal investigations are being stymied by a lack of resources. The partial government shutdown, now in its 33rd day, has become a serious national-security threat, the FBI Agents Association said on Tuesday.

Over the past several weeks, the association has been compiling stories from agents about the the shutdown’s impact on the bureau’s operations. One agent, speaking anonymously, said his unit had “lost several sources who have worked for months, and years, to penetrate groups and target subjects” due to the inability to pay confidential sources. “These assets cannot be replaced,” the agent said. “Serving my country has always been a privilege, but it has never been so hard or thankless.” Another agent reported: “Not being able to pay Confidential Human Sources risks losing them and the information they provide FOREVER. It is not a switch that we can turn on and off.”

Read: FBI agents say the shutdown is a threat to national security

Others complained that their investigations were being slow-rolled, with dozens of grand-jury subpoenas going undelivered. “The operational impacts of this shutdown are immeasurable,” said one agent in the Northeast region. “We have postponed the indictment of subjects due to the shutdown.”

President Donald Trump, who said last month that he would take responsibility for shutting the government down if Congress refused to appropriate $5.7 billion for his border wall, proposed what he described as a compromise over the weekend. But he continued to insist on the wall. Democrats rejected the proposal immediately.

The president did not mention the more than 800,000 federal workers affected by the impasse, let alone the effects it has had on counterterrorism, counterintelligence, and drug-trafficking and cybersecurity operations by the FBI—an agency for which he has little affection. In the two and a half years since the bureau launched its counterintelligence investigation into potential coordination between members of Trump’s campaign and Russia, the president has chided the FBI in dozens of tweets, rallies, and interviews. The withering morale and possibility of having to work without pay has made it difficult to recruit new agents, current and former agents have told me.

Read: The Republican Party turns against the FBI

The thousands of FBI agents and other federal employees whose unfettered work is imperative for national security have received “no assurances” about when their next paycheck will come or when they will be reimbursed for travel expenses—including overseas trips crucial to operations, one agent told me. The agent, who works in a particularly sensitive counterterrorism unit, was recently asked to travel to Africa out of his own pocket should his counterparts there need assistance.

Another agent told me that “funding for all day-to-day operations is gone. There is no rainy-day fund of cash sitting somewhere.” He wryly added that he and his colleagues are “getting about as much [information] as you are hearing from press office—very little and very late.”

An FBI spokesperson would not elaborate on the funding mechanisms available for daily operations. But she said that FBI agents and support personnel in field offices are excepted from furlough, meaning they are allowed to come to work but still won’t be paid. “FBI operations are directed towards national security and violations of federal law, and must be able to continue during a lapse in appropriations,” the spokesperson said.

Despite their best efforts to proceed with business as usual, however, agents say their investigations are being put on hold by forces out of their control, such as a lack of funds from U.S. attorneys’ offices to issue grand-jury subpoenas. “Operationally, I requested a subpoena from the U.S. attorney’s office yesterday and was told it may take a while because their legal assistants are furloughed,” one agent said. “Depending on how long the shutdown lasts, it could be several weeks before my subpoena is issued.”

The federal judiciary is running out of money, too—the Administrative Office of the U.S. Courts said in a statement on Tuesday that the federal courts can sustain funded operations through January 31, 2019 through an extension made possible by moving funds around. Courts will continue to conduct criminal trials, but some federal courts have had to issue orders “suspending or postponing civil cases in which the government is a party,” according to the statement. A federal judge in Illinois said on Tuesday that the court may run out of money to pay jurors and employees if the shutdown continues past February 8.

Ultimately, the obstacles facing FBI agents during the shutdown will have a boomerang effect on the work of the U.S. attorneys’ offices, whose federal prosecutors are “heavily dependent on law-enforcement agents for fact gathering,” said Elie Honig, a former federal prosecutor in the Southern District of New York. “Bottom line in terms of investigations: There’s very little prosecutors can do on their own if federal agents are sidelined,” he said. “Prosecutors obviously cannot execute field operations (search warrants or surveillance or arrests, for example), so without agents, those investigative avenues are completely cut off.” Honig also noted that prosecutors are trained to never speak with a witness or target without a law-enforcement agent present as a witness.

Mimi Rocah, who was also a federal prosecutor in the Southern District of New York, agreed. “It’s very hard to effectively and thoroughly work investigations and cases when the FBI is not fully functioning,” Rocah said, noting that the U.S. attorneys’ offices were dealing with their own employees not being paid and other budget constraints. “Some cases can wait, but some are urgent matters of public safety and can’t, such as anything related to violence, guns, minors, etc. But then the nonurgent cases get pushed to the back burner and things get backlogged, and that can have really lasting impacts.”

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 earlier this month, the FBI 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, the association’s president, Tom O’Connor, said that they’ll continue to do “the best with what we have.”

“But,” he added, “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.”