WASHINGTON — President Trump continued to dismantle the nation’s top domestic security agency Monday as the White House announced the imminent removal of U.S. Secret Service Director Randolph “Tex” Alles, the latest in a series of departures from the Department of Homeland Security.

A day after Secretary Kirstjen Nielsen was forced to step aside following a White House meeting with Trump, senior DHS officials remained in a fog about the fate of their agency’s leaders, expecting more firings as part of a widening purge.

“They are decapitating the entire department,” said one department official, noting that the White House had given no cause for Alles’ removal.

The instability extends to the Federal Emergency Management Agency FEMA, whose director, William “Brock” Long, left the DHS in February after supervising emergency and recovery efforts for several major natural disasters. Francis Cissna, the director of U.S. Citizenship and Immigration Services, and DHS General Counsel John Mitnick could be the next to go, DHS officials said Monday, speaking on the condition of anonymity to talk candidly of their frustrations with the White House.

Successive presidents have viewed stability at the DHS – created in the wake of the 9/11 terrorist attacks – as a top priority for national security, counterterrorism efforts and, more broadly, the country’s collective peace of mind.

With nearly two dozen agencies and subagencies, the DHS is responsible for safeguarding the country’s immigration system, cybernetworks, land borders and coasts while responding to disasters and protecting the country’s public officials.

Trump is furious about the department’s inability to reduce unauthorized migration to the United States, with one of his signature campaign issues devolving in public. But several administration officials said Monday that Trump appears to be taking out his frustrations on the entire DHS leadership, convinced he needs a full sweep.

Homeland Security Secretary Kirstjen Nielsen Associated Press/Carolyn Kaster

Further exacerbating Trump’s struggles with immigration policy on Monday was a California federal judge’s ruling to block the experimental “Remain in Mexico” program that has sent hundreds of Central American asylum seekers back across the border to wait outside U.S. territory while their asylum claims are processed.

DHS officials viewed the policy as one of Nielsen’s most significant initiatives – they were hoping to expand its use broadly across the southern border – and its halt leaves the department without one of the tools it was counting on to deter more Central American migrants from making the journey.

Sen. Ron Johnson, R-Wis., chairman of the Senate Homeland Security and Governmental Affairs Committee, said the border crisis created by the largest migration surge in a decade was being compounded by the removal of so many Homeland Security leaders in rapid succession.

“In addition to congressional dysfunction, I am concerned with growing leadership void within the department tasked with addressing some of the most significant problems facing the nation,” Johnson tweeted Monday.

No president before Trump has pushed the country’s security agencies into such a state of churning confusion, current and former DHS officials said Monday.

Last week, Trump abruptly rescinded his nomination of Ronald Vitiello to be director of U.S. Immigration and Customs Enforcement, saying he wanted to go in a “tougher” direction. Alles and Vitiello report to Nielsen.

Nielsen is scheduled to end her tenure Wednesday, when Kevin McAleenan, the current commissioner of U.S. Customs and Border Protection, takes over as acting DHS chief. His move leaves a vacancy at the top of the CBP, the country’s largest law enforcement agency.

Trump senior adviser Stephen Miller has been among the leading voices urging the president to clean house at the DHS, encouraging Trump to take wider aim at the entire department, not just the agencies responsible for immigration policy and border enforcement, White House aides said Monday.

“Immigration was the president’s signature issue, and for a variety of reasons things are spinning out of control,” said Mark Krikorian, director of the Center for Immigration Studies, a group with proposals to reduce immigration that have been influential in the Trump White House.

Krikorian said the 2020 election “isn’t that far away, and he needs to be able to show some progress” in managing the border crisis. By threatening to cut off aid to Central America and close the border with Mexico, Trump is “throwing anything against the wall to see what sticks.”

Trump named Marine Corps Gen. John Kelly to the DHS secretary role after his 2016 win, in part to reassure the country that a former reality television star would surround himself with military leaders and security experts.

Two years later, the president increasingly believes the whole leadership structure that Kelly installed is ineffective, current and former administration officials said.

One former DHS official said that when former Secretary of State Rex Tillerson left the State Department, many of the political appointees departed. But when Kelly left the DHS, most of the political appointees stayed. “They needed a big shake-up,” the former official said.

After Trump found out last week that more than 103,000 migrants arrived at the Mexico border in March – the highest total in more than a decade – he was livid, according to a White House official. The president was additionally frustrated that Nielsen and others would not close the border and change the rules to immediately stop migrants from coming to the United States to request asylum.

DHS officials are now looking for a way to satisfy the president’s demand for “tough” measures, including a plan called “binary choice” that would give migrant parents the option of remaining detained as a family or agreeing to a separation so that the child would not remain in immigration custody.

The goal of the plan would be to end the “catch and release” model that has allowed most migrant families to go free within the United States while they wait to appear before an immigration judge.

Implementing binary choice without lawmakers’ approval risks another court injunction.

“The president doesn’t like the news he’s getting on immigration, and has blamed leadership at DHS, but this is not something leadership at the department can fix,” said Stewart Baker, a top DHS adviser to President George W. Bush. “This needs to be fixed in Congress, and there doesn’t seem to be any appetite for that.”

Trump has suggested to aides in recent weeks that the administration’s previous policy of separating families at the border could be used to deter crossings and that a version of the policy could be reinstated, according to two people with knowledge of the discussions. Some aides have resisted the idea of family separations, citing the public backlash last summer and noting that Trump himself reversed it.

The president had been annoyed with Nielsen for months, even though he would occasionally give her reprieves if things went well, officials said.

Trump wanted the border closed two weeks ago but was dissuaded by Nielsen and Secretary of State Mike Pompeo, among others. Nielsen has told confidantes that she felt uncomfortable with some of the president’s requests, particularly closing the border, and that the president did not understand many of the laws governing immigration.

“He just wants drastic, drastic action,” said another White House official, adding that it is others who say: “We can’t do that.”

Trump has come to associate Alles with Kelly, whom he has frequently criticized since the chief left – particularly after Kelly made public comments Trump saw as critical of his administration. Trump also mocked Nielsen for being close to Kelly, current and former aides said.

Trump selected Alles, a retired Marine Corps general and former acting deputy commissioner of Customs and Border Protection, in 2017. He was the first Secret Service director in at least 100 years not from the agency’s ranks.

Rich Staropoli, a former Secret Service agent and former senior DHS official under Trump, said the president appears to be booting several key people who got their jobs on Kelly’s recommendation.

“He was pushed by John Kelly,” Staropoli said. “The president likes generals. But now it looks like he’s cleaning house.”

Staropoli said the number of changes in directors at the service is dizzying.

“The Secret Service is a culture that doesn’t handle change too well,” he said. “To keep changing directors – this guy’s only been there two years – isn’t a good way for the Secret Service to operate.”

“This feels like getting rid of all of the Friends of Kelly,” said Jonathan Wackrow, a former member of President Barack Obama’s detail.

Wackrow said Alles was heralded as the first “outsider” who would have a shot at fixing major security and misconduct problems that had plagued the service during the Obama administration and the early part of Trump’s tenure. But he hasn’t been able to fix some of the service’s long-standing problems, Wackrow said, including difficulty in hiring and retaining officers who help patrol the White House.

White House officials said last week’s security breach at the president’s Mar-a-Lago estate had nothing to do with Alles’ removal. In a memo to the Secret Service workforce Monday, Alles told staff reports that he’d been fired were incorrect.

“No doubt you have seen media reports regarding my ‘firing.’ I assure you that this is not the case, and in fact was told weeks ago by the Administration that transitions in leadership should be expected across the Department of Homeland Security,” Alles wrote.

James Murray, a career member of the Secret Service, will take over as director beginning in May, White House spokesperson Sarah Sanders said in a statement.