WASHINGTON (Reuters) - President Donald Trump’s administration stepped up pressure on the Department of Homeland Security (DHS) on Tuesday, raising the likelihood that he might fire more senior officials as the agency struggles with a surge of immigrants on the U.S.-Mexico border.

Two days after Homeland Security Secretary Kirstjen Nielsen announced her departure, a senior administration official said others at DHS were not doing enough to enact Trump’s promised immigration crackdown, a top priority for him since he announced his candidacy for the White House four years ago.

DHS acting Deputy Secretary Claire Grady offered her resignation to Trump, effective Wednesday, after a 28-year career at the Departments of Defense and Homeland Security, Nielsen said in a tweet late on Tuesday.

Several other DHS officials could be forced out soon, said an official familiar with the matter.

Among them were the department’s general counsel, John Mitnick, and U.S. Citizenship and Immigration Services (USCIS) Director Francis Cissna, the source said. A DHS spokesman did not respond to a request for comment on the officials’ expected tenure.

Trump denied that he was overhauling DHS and said his administration was fighting “bad laws” on immigration and a court system that “never ever rules for us” - a frequent refrain of his as a succession of policies to curb entry to the United States has been met with legal challenges by civil rights advocates.

“Nobody ever said I was cleaning house,” Trump told reporters at the White House.

Nielsen announced her resignation on Sunday after a meeting with Trump in which the two disagreed on the best way to handle border security.

The personnel changes could further destabilize the U.S. domestic security agency as it tries to stem rising numbers of immigrants arriving at the border, many of them families fleeing violence and poverty in Central America. DHS said it arrested or denied entry to more than 103,000 people along the border last month, more than double the March 2018 figure.

The U.S. Secret Service said on Monday that its chief, Randolph “Tex” Alles, would depart his job next month. Trump last Friday withdrew the nomination of Ronald Vitiello to serve as director of U.S. Immigration and Customs Enforcement.

Several top DHS jobs are either vacant or filled on an acting basis, including positions responsible for disaster response, immigration enforcement, finance, policy, and science and technology.

“It’s not good to have all these people performing in an acting position,” said Senate Homeland Security Committee Chairman Ron Johnson, a Republican.

FRUSTRATIONS

Trump has grown increasingly frustrated as DHS officials have told him that the dramatic immigration changes they seek are not possible under current law and would require the cooperation of Congress, several sources say.

Trump repeatedly pressed Nielsen over recent weeks to bring back last year’s controversial policy of separating migrant children from their parents, one source said. Trump abandoned that policy last year in the face of widespread public outrage, and it was subsequently struck down in court.

Trump denied on Tuesday that he was reviving the separation policy. Johnson said that policy would have “no support” in Congress.

A senior administration official, speaking on condition of anonymity, said one option may be to give migrant families a choice of staying in long-term detention together while they await a court hearing or splitting up, an idea known as “binary choice.”

U.S. Homeland Security official Claire Grady attends a news conference during a meeting of the Interior ministers of G7 nations in Paris, France, April 5, 2019. REUTERS/Charles Platiau

The administration may also move to detain migrant children for longer than the 20-day maximum set by a court ruling, to spur a legal challenge that could overturn that limit, the official said.

The official said DHS has been too slow in drafting new rules that would tighten immigration.

The official singled out USCIS, saying it had not moved quickly enough to tighten H-1B visas for skilled workers and has granted an “astronomical” number of asylum claims.

Asylum officers found that applicants had a “credible fear” of persecution in their home countries in 78 percent of the cases they decided between October and February, according to USCIS data.

The White House could anger allies in Congress if it fires USCIS head Cissna, who previously worked with Republicans on the Senate Judiciary Committee. Republican Senator Chuck Grassley said on Twitter that Cissna was “doing what voters asked4 w PresTrump election.”

Any move to fire Cissna or other DHS leaders would likely complicate the department’s leadership woes.

U.S. Customs and Border Protection Commissioner Kevin McAleenan is due to take Nielsen’s place on a temporary basis, starting on Wednesday, leaving DHS without a permanent leader on the front lines of the border crisis.

DHS’s acting deputy secretary Grady was legally supposed to take over after Nielsen’s departure, so Grady’s resignation on Tuesday cleared the way for McAleenan to take the agency’s reins.

Trump has interviewed several candidates for the top job over the past week and a half, including former Kansas Secretary of State Kris Kobach, former Virginia attorney general Ken Cuccinelli, and former acting Immigrations and Customs Enforcement head Thomas Homan.

All three have expressed hard-line views on illegal immigration, and could have difficulty winning confirmation in the U.S. Senate, which Trump’s Republicans control by a 53-47 margin.

Senate Republican Leader Mitch McConnell said Congress needed to set aside its differences to overhaul immigration laws, which it has repeatedly failed to do over the past 15 years.