The rule of law is undergoing a "major breakdown", according to a former member of staff at the Department of Justice.

Donald Trump's decision to fire attorney general Sally Yates – who was forced out after questioning whether the controversial Muslim ban is legal, and refusing to defend it in court – violates a "principle that everything else in our democracy depends on", according to Matthew Miller. Mr Miller served as director of public affairs at the US DoJ, and echoed the opinions of a range of commentators in criticising the decision to sack Ms Yates.

"In our democracy, the president is not supposed to dictate to the [attorney general] how to interpret the law," he wrote on Twitter. "This is a major breakdown in the rule of law.

Donald Trump sacks acting attorney general over immigration ban

"A president who fires an AG over this will think he can fire an AG over, say, a probe into whether his campaign coordinated [with] Russia."

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He criticised the decision to replace Ms Yates with Dana Boente, the US Attorney for the Eastern District of Virginia, who was sworn in at a private ceremony and immediately. He is thought to be much less opposed to Mr Trump than Ms Yates, who had served under President Obama.

“I am honoured to serve President Trump in this role," Mr Boente said when he was appointed. "I will defend and enforce the laws of our country to ensure that our people and our nation are protected."

Mr Boente pondered whether the Trump administration had chosen Mr Boente precisely because he would follow orders.

"The next US [attorney] in line of succession was not Boente, but Zach Fardon," he wrote. "Did Trump go forum shopping for one who would follow orders?"

He said that people should oppose the move no matter how they feel about the Executive Order that banned refugees and people from seven Muslim-majority countries from entering the US.

"No matter what you think about the EO, the independence of DOJ is a principle that everything else in our democracy depends on," he wrote.

Lawyer and constitutional expert David Allen green echoed the comments, hailing Sally Yates as a hero.

"Far from "betraying" the @theJusticeDept, Sally Yates chose not to betray the Rule of Law," he wrote on Twitter, in reference to comments in the press release from Donald Trump. "A legal hero."