President Donald Trump fired Acting Attorney General Sally Yates Monday night, after Yates ordered Justice Department lawyers Monday not to defend his immigration order temporarily banning entry into the United States for citizens of seven Muslim-majority countries and refugees from around the world.

In a press release, the White House said Yates had โ€œbetrayed the Department of Justice by refusing to enforce a legal order designed to protect the citizens of the United States.โ€

The White House has named Dana Boente, U.S. attorney for the Eastern District of Virginia, as acting attorney general. Boente told The Washington Post that he will agree to enforce the immigration order.

Earlier on Monday, Yates ordered Justice Department not to defend President Trumpโ€™s immigration order temporarily banning entry into the United States for citizens of seven Muslim-majority countries and refugees from around the world, declaring in a memo that she is not convinced the order is lawful.

Yates wrote that, as the leader of the Justice Department, she must ensure that the departmentโ€™s position is โ€œlegally defensibleโ€ and โ€œconsistent with this institutionโ€™s solemn obligation to always seek justice and stand for what is right.โ€

โ€œAt present, I am not convinced that the defense of the Executive Order is consistent with these responsibilities nor am I convinced that the Executive Order is lawful,โ€ Yates wrote. She wrote that โ€œfor as long as I am the Acting Attorney General, the Department of Justice will not present arguments in defense of the Executive Order, unless and until I become convinced that it is appropriate to do so.โ€

Yates is a holdover from the Obama administration, but the move nonetheless marks a stunning dissent to the presidentโ€™s directive from someone who would be on the front lines of implementing it.

Also Monday, State Department diplomats circulated various drafts of a memo objecting to Trumpโ€™s order, which was issued Friday. The document is destined for whatโ€™s known as the departmentโ€™s Dissent Channel, which was set up during the Vietnam War as a way for diplomats to signal to senior leadership their disagreement on foreign policy decisions.

More than 100 diplomats have signed the memo, which argues that the immigration ban will not deter attacks on American soil but will generate ill will toward U.S. citizens.

What will happen next is unclear. Sen. Jeff Sessions (R-Ala.), Trumpโ€™s attorney general nominee, could be confirmed as early as Thursday or Friday. The Senate Judiciary Committee is scheduled to consider his nomination today, and the entire Senate must wait one day before voting.

A spokeswoman for Sessions declined to comment. A White House spokeswoman did not immediately return an email seeking comment.

White House domestic policy adviser Stephen Miller said on MSNBC that Yatesโ€™s decision was โ€œa further demonstration of how politicized our legal system has become.โ€

โ€œItโ€™s sad that our politics have become so politicized that you have people refusing to enforce our laws,โ€ Miller said.

A Justice Department official familiar with the matter said Yates felt she was in an โ€œimpossible situationโ€ and had been struggling with what to do about a measure she did not consider lawful.

A Justice official confirmed over the weekend that the departmentโ€™s office of legal counsel had been asked to review the measure to determine if it was โ€œon its face lawful and properly drafted.โ€

In her memo, though, Yates said her role was broader. She wrote that an office of legal counsel review does โ€œnot address whether any policy choice embodied in an Executive Order is wise or just,โ€ nor does it โ€œtake account of statements made by an administration or its surrogates close in time to the issuance of an Executive Order that may bear on the orderโ€™s purpose.โ€

That could be a reference to Trumpโ€™s campaign trail comments about a โ€œMuslim banโ€ or the recent assertion by Trump surrogate Rudolph W. Giuliani that the president had asked him โ€œthe right way to do it legally.โ€

Yatesโ€™s memo came as civil rights lawyers and others across the country increased the pressure on Trump on Monday to dial back the ban – filing or threatening to file legal challenges to the executive order as they worked to determine if people were still being improperly denied entry or detained.

The defiant legal conclusion from the countryโ€™s top law enforcement official will surely boost their arguments. Lee Gelernt, deputy director of the ACLUโ€™s Immigrantsโ€™ Rights Project, who worked on one of the legal challenges, said, โ€œIt sends a very strong message that thereโ€™s something very wrong with the Muslim ban.โ€

Just days after stepping down from office, former president Barack Obama weighed in through a spokesman, seeming to back those demonstrating against Trumpโ€™s decree and declaring his opposition to โ€œdiscriminating against individuals because of their faith or religion.โ€

Obama said that he was โ€œheartened by the level of engagement taking place in communities around the countryโ€ โ€” an apparent reference to protests at airports nationwide.

He also disputed Trumpโ€™s claim that his ban was based on Obama administration decisions.

Separately, more than 100 former Cabinet secretaries and senior national security and military officials from the Obama, George W. Bush and other administrations called on the current and acting heads of the Departments of Justice, State and Homeland Security to dial back enforcement of the order.

But George J. Terwilliger III, a deputy attorney general in the George H.W. Bush administration, said Yatesโ€™s memo was a โ€œfoolish, naked political move by what appears to be an ambitious holdover officialโ€ that would only create โ€œunnecessary disorder.โ€

โ€œShe has to be asked to resign immediately,โ€ Terwilliger said. โ€œLook, the executive branch of our government is unitary. Thereโ€™s only one boss, and that boss has spoken. If some subordinate official thinks that his direction is illegal, than the choice is to resign.โ€

Even as Yates issued her memo, civil rights advocates said they still had significant questions about how the executive order was being enforced and even who it might be affecting.

A lawsuit in Virginia claimed that dozens of people may have been forced to give up their green cards by Customs and Border Protection agents, though that figure could not immediately be substantiated. Lawyers in Los Angeles said they had received similar reports, though they were still exploring them.

Lawyers were also working to determine if anyone might still be in custody.

The ACLUโ€™s Gelernt said that lawyers were โ€œhaving trouble independently verifying anything because the government will not provide full access to all the detainees.โ€ Of particular concern, he said, was that the government had not turned over a list of detainees, as it had been ordered to do by a federal judge in New York. He said lawyers might be back in federal court in the next day or so to forcibly get access to it.

The ACLUโ€™s suit in New York is perhaps the most significant of a growing number of legal challenges to the order. The Council on American-Islamic Relations also filed a sweeping challenge Monday, alleging that the order is meant โ€œto initiate the mass expulsion of immigrant and non-immigrant Muslims lawfully residing in the United States.โ€ The lawsuit lists 27 plaintiffs, many of them lawful permanent residents and refugees who allege that Trumpโ€™s order will deny them citizenship or prevent them from traveling abroad and returning home. Lawyers with the Northwest Immigrant Rights Project filed a similar challenge in Washington state.

Bob Ferguson, Washington stateโ€™s attorney general, said Monday that he, too, plans to file a federal lawsuit seeking an immediate halt to the orderโ€™s implementation – making him the first state official to do so. That lawsuit has the support of Microsoft and Amazon, two companies based in Washington state. (Amazon owner Jeffrey P. Bezos owns The Washington Post in his personal capacity and has voiced Amazonโ€™s opposition to the order personally).

The White House, meanwhile, continued to defend Trumpโ€™s executive order. White House press secretary Sean Spicer said that one lawsuit โ€œdoesnโ€™t make any senseโ€ and sought to minimize the action as simply subjecting 109 people to more rigorous screening.

According to State Department statistics, about 90,000 people received nonimmigrant or immigrant visas in fiscal year 2015 from the seven countries affected by Trumpโ€™s executive order.