Yates said her response to the Trump administration’s travel ban was such a moment for her. She was fired by President Donald Trump in January after refusing to defend the ban in court.

“I was in the car on the way to the airport late in the afternoon on Friday, January 27 when I learned from media reports that the president had signed an executive order restricting travel from seven Muslim majority countries,” she recalled. “It was the first we’d heard of it, but we knew we’d need Department of Justice lawyers in courts all over the country defending it within a matter of hours.”

Subscribe to The World’s Most Powerful Women, Fortune’s daily must-read for global businesswomen.

The following Monday, she learned that the DOJ had to take a position on the constitutionality of the order. Ultimately, she said, she concluded that defending the ban “would require the DOJ to argue that the executive order had nothing to do with religion, that it was not intended to disfavor Muslims.” This would have to be done, she said, “despite the numerous prior statements that had been made by the president and his surrogates regarding his intent to effectuate a Muslim ban.”

[youtube https://www.youtube.com/watch?v=F2FMZFzX84k]

“I believed this would require us to advance a pretext; a defense not grounded in truth. And so I directed the Department of Justice not to defend the ban,” she told graduates. That decision eventually led to her firing. Since then, she’s also been embroiled in on-going investigations of Russian meddling in the 2016 election. She has said publicly that she warned the White House about conduct by Michael Flynn that made the then-national security advisor—a key player in the on-going investigation—susceptible to Russian blackmailing. The White House did not act on that information immediately, keeping Flynn on for another 18 days before he stepped down on February 13.

Yates said on Wednesday that the travel ban was “an unexpected moment when law and conscience intersected and a decision had to be made in a very short period of time.” She said her 27-year tenure at the DOJ and input from mentors and colleagues shaped how she responded.

“Over the course of your life and your career you too will face weighty decisions where the law and conscience intertwine and while it may not play out in such a public way, the conflict that you’ll feel will be no less real,” she said. “The time for introspection is all along the way; to develop who you are and what you stand for because you never know when you’re going to be called to answer that question.”