Sally Yates
Sally YatesReuters

U.S. President Donald Trump on Monday night fired acting Attorney General Sally Yates, after she instructed Justice Department lawyers not to make legal arguments defending his executive order on immigration and refugees.

"The acting Attorney General, Sally Yates, has betrayed the Department of Justice by refusing to enforce a legal order designed to protect the citizens of the United States. This order was approved as to form and legality by the Department of Justice Office of Legal Counsel," said a White House statement quoted by Politico.

"Ms. Yates is an Obama Administration appointee who is weak on borders and very weak on illegal immigration," the statement added.

Yates was appointed by former President Barack Obama and would have served until Sen. Jeff Sessions, Trump's nominee for attorney general, is confirmed.

She will be replaced with the U.S. Attorney in Alexandria, Virginia, Dana Boente.

In a letter to lawyers sent earlier Monday, Yates wrote, "My responsibility is to ensure that the position of the Department of Justice is not only legally defensible, but is informed by our best view of what the law is after consideration of all the facts.”

"In addition, 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," she added.

Trump's executive order, signed Friday, bars citizens of seven Muslim-majority countries from entering the United States for the next 90 days, suspends the admission of all refugees for 120 days and indefinitely suspends the Syrian refugee program.

Yates' decision not to defend it came amid a flood of protests against the executive order nationwide and after four federal judges ruled against Trump's order, staying its impact on people who were detained at U.S. airports over the weekend.

On Sunday, 16 Democratic state attorneys general blasted the executive order, vowing to fight it and calling his demands “unconstitutional, un-American and unlawful.”

Yates wrote in her letter, according to CNN, "At 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.”

White House policy director Stephen Miller, who helped craft the executive order, called Yates' decision "a further demonstration of how politicized our legal system has become."

"It's sad that our politics have become so politicized, that you have people refusing to enforce our laws," Miller said Monday night on MSNBC.

Trump clarified on Sunday that the executive order is about security and is not a Muslim ban.

"America is a proud nation of immigrants and we will continue to show compassion to those feeling oppression, but we will do so while protecting our own citizens and border," he said, adding, "To be clear, this is not a Muslim ban, as the media is falsely reporting. This is not about religion - this is about terror and keeping our country safe.”