The Department of Homeland Security gave no reason for the abrupt removal of Daniel Ragsdale, the acting director of US Immigration and Customs Enforcement (ICE), on Monday night.
The lawyer has returned to his previous post as deputy director of the ICE, where he has worked for 11 years advising its enforcement programmes.
Mr Ragsdale’s replacement puts the postition of acting deputy director Peter T Edge and other officials in doubt at the agency, which is charged with enforcing Mr Trump’s executive order temporarily banning refugees and citizens of seven predominantly Muslim countries.
John F Kelly, the Secretary of Homeland Security, was reportedly still discussing the proposals with officials when an aide looked up to find the President was already signing the order on live television.
In a statement, he said Mr Trump appointed Thomas D Homan as the new acting director of ICE, where he was previously the executive associate director of its enforcement and removal operations.
“In this capacity, he led ICE’s efforts to identify, arrest, detain, and remove illegal aliens, including those who present a danger to national security or are a risk to public safety, as well as those who enter the United States illegally,” Mr Kelly said.
“I look forward to working alongside him to ensure that we enforce our immigration laws in the interior of the United States consistent with the national interest.”
Mr Homan has served as a police officer in New York, border patrol officer and special immigration agent, later heading up the division in Dallas, Texas.
News of his appointment came hours after Mr Trump fired the acting Attorney General for “betraying the Department of Justice” after she refused to enforce his executive order.
In a statement confirming Ms Yates’ replacement with Dana Boente, he called her "weak on borders and very weak on illegal immigration” amid global protests against his incendiary policy.
“Calling for tougher vetting for individuals travelling from seven dangerous places is not extreme,” Mr Trump said. “It is reasonable and necessary to protect our country.”
Ms Boente will serve as acting Attorney General until Jeff Sessions is confirmed by the Senate, where the President claimed he was being “wrongly held up by Democrat senators for strictly political reasons”.
His appointment has been dogged by controversy after it emerged he was denied a role as a federal judge because of allegations of racial discrimination in the 1980s.
The chain of events on Monday has been compared to the Nixon-era “Saturday Night Massacre” in the US, when the Attorney General and his deputy resigned rather than follow orders to fire a special prosecutor investigating the Watergate scandal.
At least three top national security officials - Defence Secretary Jim Mattis, Homeland Security Secretary Mr Kelly and Rex Tillerson, who is awaiting confirmation to lead the State Department - have told associates they were not aware of details of the executive order on immigration until Mr Trump signed it.
Leading intelligence officials were also left largely in the dark, according to reports, as was the Senate Foreign Relations Committee.
Amid demonstrations and legal challenges, there are signs of growing internal dissent over the President’s executive order, which pauses the US refugee programme for four months, bans Syrian refugees indefinitely and freezes immigration from Iraq, Syria, Iran, Sudan, Libya, Somalia and Yemen for 90 days.
Federal judges in New York and several other states have issued orders that temporarily block the government from deporting people with valid visas who arrived after Mr Trump's travel ban took effect and found themselves in limbo.
After a chaotic weekend during which permanent residents were among those detained at airports, the Department of Homeland Security clarified that customs and border agents should allow legal residents to enter the country.
The Pentagon is also trying to exempt Iraqis who worked alongside the US and coalition forces at extreme risk during the ongoing conflict.
Ms Yates concluded that the policy was at odds with the Justice Department's mission and said that though other lawyers had reviewed the order, they had not examined whether it was "wise or just".
“I am responsible for ensuring that the positions we take in court remain consistent with this institution's solemn obligation to always seek justice and stand for what is right,” the acting Attorney General wrote in a letter before she was fired, directing government lawyers not to defend the order.
White House spokesman Sean Spicer challenged others opposed to the measure to resign. “They should either get with the program or they can go,” he said.
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