Accusing her of betrayal and insubordination, Donald Trump fired acting US Attorney General Sally Yates after she publicly questioned whether his controversial refugee and immigration ban was constitutional and refused to defend it in court.
The dramatic public clash between the new president and the nation's top law enforcement officer laid bare the growing discord and dissent surrounding his executive order, which temporarily halted the entire US refugee program and banned all entries from seven Muslim-majority nations for 90 days.
The move refusing entry to those from Syria, Lybia, Iraq, Iran, Yemen, Somalia, and Sudan, set off massive protests at airports across the country.
After the Trump administration suffered its first defeat in federal court over the weekend, staying some aspects of the executive order, Ms Yates issued her denouncement of the action. The President fired her shortly afterwards.
The White House said in a statement that Ms Yates had "betrayed the Department of Justice by refusing to enforce a legal order designed to protect the citizens of the United States."
He immediately named longtime federal prosecutor Dana Boente, the US Attorney for the Eastern District of Virginia, as Yates' replacement.
Mr Boente was sworn in privately, the White House said.
He promptly order Justice Department lawyers to "do our sworn duty and to defend the lawful orders of our President."
He said: “I am honoured to serve President Trump in this role.... I will defend and enforce the laws of our country to ensure that our people and our nation are protected."
Senator Jeff Sessions, Mr Trump's pick for attorney general, will almost certainly defend the policy once he's sworn in.
He's expected to be confirmed by the Senate Judiciary Committee and could be approved within days by the full Senate.
Ms Yates, a Democrat who was appointed by the Obama administration had earlier order lawyers not to defend Mr Trump's order.
"I am responsible for ensuring that the positions we take in court remain consistent with the institution's solemn obligation to always seek justice and stand for what's right," she said.
"At the present, I am not convinced that the defence of the executive order is consistent with these responsibilities, nor am I convinced that the executive order is lawful."
The former Acting Attorney General was the first person to be fired on principle by the Trump administration.
Ms Yates, the highest ranked Senate-approved Justice Department lawyer was the only person with the authority to approve international surveillance warrants.
Press Secretary Sean Spicer had earlier challenged government employees to leave their posts when questioned about US diplomats who issued a dissent memo draft condemning Mr Trump's executive order.
"Any government official who doesn’t understand the President’s goals in this and exactly what it was,” he told reporters, “they should either get with the programme, or they can go."
Former President Barack Obama has also defied custom and spoken out against Mr Trump's order – referred to by civil rights advocates as the "Muslim Exclusion Order". The former president said he was "heartened" to see such civic engagement as Americans take to the streets to denounce the new President.
"Citizens exercising their Constitutional right to assemble, organise and have their voices heard by their elected officials is exactly what we expect to see when American values are at stake," a statement from Mr Obama’s spokesperson said.
"With regard to comparisons to President Obama’s foreign policy decisions, as we’ve heard before," the statement added. "The President fundamentally disagrees with the notion of discriminating against individuals because of their faith."
Meanwhile, the state of Washington his filed a lawsuit against the Trump administration for the refugee ban.
"We are a country based on the rule of law, and in a courtroom it is not the loudest voice that prevails, it's the Constitution," the state's Attorney General Bob Ferguson said at a news conference.
"At the end of the day, either you're abiding by the Constitution or you are not. And in our view, the President is not adhering to the Constitution when it comes to this executive action."