President Donald Trump shared with the country on Monday morning over Twitter that he had fired Defense Secretary Mark T. Esper. This is the third defense secretary who Trump has fired in his term as president.

Trump wrote that Esper would be temporarily replaced with the “highly respected” director of the National Counterterrorism Center, Christopher C. Miller. Miller has previously served in Trump’s White House as the top counterterrorism policy official, is a former Army Green Beret, and has already been approved by the Senate for the position of Defense Secretary.

Esper’s termination was not completely unexpected. In June, when Trump wanted to use the Insurrection Act to send in active military troops to cities heavy with protestors, Esper publicly went against him. Esper first spoke of his disagreement in a news conference in June, and reportedly caused Trump to fly into a rage.

Although a spokesman for the defense secretary tried to cover for him after his initial disagreements with the president, Esper seemed to bury himself deeper, working to eliminate the display of the Confederate flag (without specifically naming “Confederate” in context) on U.S. military bases internationally. Trump has strongly disagreed with efforts to eliminate the use of the Confederate flag.

Esper has also gone to great efforts to make sure that he and his department adhere to the Centers for Disease Control and Prevention’s guidelines on social distancing, mask-wearing and all other rules regarding the coronavirus.

“It is tedious – I understand that,” said Esper at a virtual town-hall. “But I think it’s showing, in terms of the Navy’s results in terms of infection rates, that they’re doing a very good job.” Esper’s opinions on COVID-19 differ greatly from those of Trump’s, who has said before that wearing a mask is a sign of weakness.