U.S. President Donald Trump fired his defense secretary, Mark Esper, on Monday, two days after his election loss to former Vice President Joe Biden. 

Trump announced the replacement of the defense chief in a Twitter post, saying that Esper has been terminated and then thanking him for his service.

Trump said Christopher C. Miller, the current director of the National Counterterrorism Center, will be acting secretary of defense, effectively immediately, adding he will do a great job. 

Trump and Esper have clashed over a number of issues, including deploying the military to deal with protests over racial injustice earlier this year.

The dismissal is seen as a sign that Trump plans to be active for the next two-and-a-half months and that the transition to the new Biden administration is going to be turbulent.