The Dean of the Elliott School of International Affairs labeled President Donald Trump a “Nazi- and white-nationalist sympathizer” and called on the president’s closest advisers to denounce him in a blistering op-ed published Thursday on the news website Foreign Policy.

Reuben Brigety, the school’s dean, wrote that Trump’s remarks blaming “both sides” for the violence at a white nationalist rally Saturday in Charlottesville, Va. were “positively revolting.”

“Events in the aftermath of the violence in Charlottesville have made this abundantly clear. For the first time in our history, a Nazi sympathizer occupies the Oval Office,” Brigety wrote.

Brigety criticized Trump for initially refusing to call out white supremacists and neo-Nazis by name the day a man reported to be obsessed with Nazis allegedly drove a car into a group of counter-protesters in Charlottesville, killing one person. Under pressure, Trump did condemn those groups in a statement Monday, but the following day he suggested there were “good people” among the crowd of Confederate and Nazi-flag waving demonstrators.

“In essence, Trump definitively showed the world who he is,” Brigety wrote in the op-ed. “And we should believe him.”

Brigety, who served as the U.S. ambassador to the African Union during the Obama administration, said Trump’s remarks were a defense of white supremacists and called on several members of Trump’s inner-circle, including Attorney General Jeff Sessions and Defense Secretary James Mattis, to reject Trump’s views even it costs them their jobs in the administration.

“Either you challenge the president’s blatant racism, or you acquiesce to his repugnant views to the detriment of your credibility with those you lead and to your own sense of personal honor,” he wrote.

He said there are three choices before members of Trump’s cabinet: resign, speak out or silently serve.

“And how, gentlemen, can you continue to rationalize serving a man who so consistently tramples on the most basic values of our country that each of you, in your own way, has spent a lifetime serving?,” Brigety wrote.

The Elliott School shared Brigety’s op-ed in a post on the school’s official Facebook page.

Brigety’s statement was the strongest made by a University official in the wake of the events in Charlottesville. University President Thomas LeBlanc condemned violence and hatred in a statement earlier this week that didn’t directly mention Trump.