"All arguments have to be based on truth," Yates said during testimony before a Senate panel. "We're not just a law firm. We're the Department of Justice."
In response to questions from two Texas Republicans at a Senate Judiciary subcommittee hearing, Yates painted a picture of a White House that kept the Department of Justice out of the loop ahead of the executive order's release.
Sen. John Cornyn said her actions with regard to the executive order were "enormously disappointing" and accused her of undermining the powers of the President because she disagreed with Trump's order "as a policy matter."
Yates told Cornyn that her actions were not done "purely as a policy matter" and cited her confirmation hearing, where she was asked about enforcing actions she viewed as against the law.
"I made a determination that I believed that it was unlawful," Yates said. "I also thought that it was inconsistent with the principles of the Department of Justice, and I said 'no.' And that's what I promised you I would do, and that's what I did."
Later on in the hearing, Yates and Sen. Ted Cruz got into a back-and-forth over her disagreement with a decision by the department's Office of Legal Counsel that defended the order.
Yates said that although the office concluded the order was lawful, the office's focus was "narrow" and ignored contextual factors that she said undermined the legality of the order.
"In this particular instance, particularly where we were talking about a fundamental issue of religious freedom -- not the interpretation of some arcane statute, but religious freedom -- it was appropriate for us to look at the intent behind the President's actions," Yates said.
Cruz asked, "In the over 200 years of the Department of Justice history, are you aware of any instance in which the Department of Justice has formally approved the legality of a policy, and three days later the attorney general has directed the department not to follow that policy and to defy that policy?"
"I'm not," Yates responded. "But I'm also not aware of a situation where the office of legal counsel was advised not to tell the attorney general about it until after it was over."
"I would note that might be the case if there's reason to suspect partisanship," Cruz said.
On CNN's "Erin Burnett OutFront," Democratic Sen. Sheldon Whitehouse criticized Cruz for his comments alleging that Yates was motivated by partisanship.
"I think it's not only wrong," Whitehouse said. "I think it's really low. This is a woman who has worked in the Department of Justice under Republican and Democratic administrations without blemish for 27 years."
In an exchange with Democratic Sen. Amy Klobuchar, Yates said she did not know about the travel ban before it was issued.
"I learned about this from media reports," Yates said.
During his campaign, Trump called for "a total and complete shutdown of Muslims entering the United States until our country's representatives can figure out what is going on." Although the White House has denied Trump's two attempts to issue travel bans were in fact Muslim bans, many have pointed to his campaign rhetoric to argue the orders were just that.
Shortly after Trump issued his first travel ban, Yates directed the Justice Department not to enforce it. Trump promptly fired her and appointed US Attorney Dana Boente to take her place until the Senate confirmed Jeff Sessions to be attorney general.
Yates was an Obama appointee whom Trump asked to stay on as the temporary head of the Justice Department.
She also emerged as a major figure in the controversy surrounding retired Gen. Michael Flynn's short time as national security adviser, and appeared before the subcommittee on Monday to testify about alleged Russian attempts to interfere
in the 2016 election.