Former Deputy Attorney General Sally Yates defiantly proclaimed that President Trump has taken his "assault on the rule of law to a new level" after he demanded that the Department of Justice (DOJ) investigate allegations of severe misconduct and potential espionage during his 2016 presidential campaign.

In a Sunday tweet, Trump said "I hereby demand, and will do so officially tomorrow, that the Department of Justice look into whether or not the FBI/DOJ infiltrated or surveilled the Trump Campaign for Political Purposes - and if any such demands or requests were made by people within the Obama Administration!"

I hereby demand, and will do so officially tomorrow, that the Department of Justice look into whether or not the FBI/DOJ infiltrated or surveilled the Trump Campaign for Political Purposes - and if any such demands or requests were made by people within the Obama Administration! — Donald J. Trump (@realDonaldTrump) May 20, 2018

Yates, who was fired last year by Trump after she refused to back his controversial "travel ban" which would have temporarily restricted travel into the United States from seven countries with ties to terrorism. The former Deputy AG warned that Trump's demand to investigate the DOJ "crossed a line."

“ 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."

“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," added Yates. “I think [Deputy Attorney General] Rod Rosenstein 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 says that the Justice Department is becoming more and more accustomed to Trump's behavior, which 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.”

Earlier Monday, former Attorney General Eric Holder tweeted (with uncharacteristically poor grammar) "Trump demand for DOJ investigation is dangerous/democracy threatening. DOJ response is disappointing.There is no basis/no predicate for an inquiry.It ’s time to stand for time honored DOJ independence.That separation from White House is a critical part of our system."

Trump demand for DOJ investigation is dangerous/democracy threatening. DOJ response is disappointing.There is no basis/no predicate for an https://t.co/UZn0rCUpcK’s time to stand for time honored DOJ independence.That separation from White House is a critical part of our system. — Eric Holder (@EricHolder) May 21, 2018

Meanwhile, Yates said Trump had been "tearing down the legitimacy" of the DOJ - warning that his attacks on officials such as AG Jeff Sessions and special counsel Robert Mueller are "not normal" - and are becoming normalized.