Former Deputy Attorney General Sally YatesSally Caroline YatesMerriam-Webster: A 200-year-old dictionary offers hot political takes on Twitter Sally Yates: Moral fiber of US being 'shredded by unapologetic racism' Trump: 'Impossible for me to know' extent of Flynn investigation MORE on Monday said President TrumpDonald John TrumpJimmy Carter: 'I hope there's an age limit' on presidency White House fires DHS general counsel: report Trump to cap California trip with visit to the border MORE has taken his “assault on the rule of law to a new level” by demanding the Justice Department (DOJ) look into alleged surveillance abuses of his 2016 presidential campaign.

Yates, whom Trump fired last year after she refused to defend his travel ban targeting several Muslim-majority countries, warned that he crossed a new line by asking the department on Twitter over the weekend to investigate whether the FBI surveilled his campaign for "inappropriate purposes.”

“I think what we’re seeing here is the president has taken his all-out assault of the rule of law to a new level and this time he is ordering up an investigation of the investigators who are examining his own campaign. You know, that’s really shocking,” Yates said on MSNBC's "Morning Joe."

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“I know it was just a tweet but he did say something to the effect of, if I recall correctly, ‘I hereby order.’ And we saw the Justice Department respond to that," Yates added. “I think [Deputy Attorney General] Rod RosensteinRod RosensteinHouse Democrats seeking Sessions's testimony in impeachment probe McCabe's counsel presses US attorney on whether grand jury decided not to indict US attorney recommends moving forward with charges against McCabe after DOJ rejects his appeal MORE is trying to strike a balance here between defusing the situation and also protecting the rule of law and the institutional integrity of the department.”

Yates also cautioned that the Justice Department becoming more accustomed to Trump’s actions and statements could threaten the rule of law.

“We become accustomed to things that the president does, in directing DOJ,” Yates said. “You know, I can remember a time when he would issue a tweet or directive and the reports would be: ‘In an unprecedented act, the president did X or Y.’ It’s not so unprecedented anymore and oftentimes it doesn’t even make it through the full 24-hour news cycle.”

Yates has spoken out against the president's attacks on the Justice Department in the past.

Earlier this month, Yates said Trump was "tearing down the legitimacy” of the agency, warning that his attacks on top officials like Attorney General Jeff Sessions and special counsel Robert Mueller are “not normal,” but are becoming normalized.