With President Trump's attorney general nominee, Jeff Sessions, still awaiting Senate confirmation, Sally Yates, a holdover from President Obama's administration, has been running the Justice Department.

And in a dramatic statement Monday night, Yates announced that she was instructing department lawyers not to defend Trump's executive order — which restricts entry into the US by refugees and nationals of seven majority-Muslim countries — from court challenges.

“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,” Yates wrote. “Consequently, for 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.”

Trump responded by firing Yates. In a statement later Monday night, the White House announced her position would be filled by Dana Boente, US attorney for the Eastern District of Virginia. Boente told Washington Post reporter Matt Zapotosky that he would defend the order in court “appropriately and properly.”

Remarkably for a sitting president, the White House didn’t just announce Yates’s firing but also attacked her personally, calling her “an Obama Administration appointee who is weak on borders and very weak on illegal immigration” who “betrayed the Department of Justice.”

Here is Yates's letter:

Acting Attorney General tells Justice Dept. lawyers not to defend Trump's immigration order, concerned it's not legal. Here is her letter. pic.twitter.com/f6EX7XWCTO — Bradd Jaffy (@BraddJaffy) January 30, 2017

And here is the White House statement announcing her firing:

The Trump White House skipped the standard vetting and policy development process

White House adviser Stephen Miller — reportedly a key architect of the executive order — went on MSNBC Monday to say that Yates's move was "a further demonstration of how politicized our legal system has become," and that it was a "misguided political protest."

Yates’s move, principled though it might have been, was a display of dissent by an Obama administration official who was on her way out anyway. Still, this is a very unusual event, since transitions between presidents have generally run smoothly in different years.

Overall, Trump bears a lot of the blame here. He chose to issue the executive order without going through the ordinary interagency process — meaning he didn’t thoroughly vet it with the agencies that are tasked with implementing it. The New York Times reported that Homeland Security Secretary John Kelly got his first full briefing on the order while Trump was in the process of signing it, and that Defense Secretary James Mattis “was not consulted by the White House” or “given an opportunity to provide input.”

Trump didn’t wait for his appointees to be confirmed, either. Obama administration holdovers are currently running 13 of the main Cabinet agencies, including the State Department and Treasury Department, so it is very possible we will see other decisions conflicting with the president's preferences on this matter while his nominees await confirmation.

Sessions is expected to win confirmation in the near future (he faces a Senate committee vote tomorrow). Still, parts of the immigration order are being contested in court now, so things are obviously quite messy. And overall, it's another setback for the president after a chaotic weekend.