Former Deputy Attorney General Sally YatesSally Caroline YatesSally Yates: I never thought that I'd be saying, 'Yeah, go Liz Cheney' ABC lands first one-on-one TV interview with Garland since confirmation Appointing a credible, non-partisan Jan. 6 commission should not be difficult MORE on Monday said President TrumpDonald Trump Pence said he's 'proud' Congress certified Biden's win on Jan. 6 Americans put the most trust in their doctor for COVID-19 information: poll OVERNIGHT DEFENSE: Biden administration to evacuate Afghans who helped US l Serious differences remain between US and Iran on nuclear talks l US, Turkish officials meet to discuss security plans for Afghan airport 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 Judiciary to probe DOJ's seizure of data from lawmakers, journalists The Hill's Morning Report - Biden-Putin meeting to dominate the week Media leaders to meet with Garland to discuss leak investigations 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.