President Trump announced the ouster of Defense Secretary Mark T. Esper on Monday, marking the exit of Trump’s fourth Pentagon chief and naming a senior intelligence official to take his place.

“Mark Esper has been terminated. I would like to thank him for his service,” the president said on Twitter.

Trump said that Christopher Miller, head of the National Counterterrorism Center, would immediately become acting defense secretary. “Chris will do a GREAT job!” Trump said.

Esper’s firing, expected since at least June but announced suddenly as Trump continues to contest the results of the presidential election, plunges the Pentagon into another period of leadership upheaval as military officials seek to reorient the military toward threats emanating from Asia and navigate political tensions at home….