On Tuesday, US President Donald Trump appointed his loyalists to key positions in the Pentagon, after sacking Defense Secretary Mark Esper, according to Sky News agency.
Trump announced his dismissal of Esper on Twitter on Monday, in a sign that he may use his final months in office to settle scores within his administration.
In the wake of Esper's departure, the Pentagon's top policy adviser resigned, and the US president promoted Anthony Tata, a retired army brigadier general, who had previously described Obama as a "terrorist leader," according to the Associated Press.
Esper was replaced by Christopher Miller, who had been the director of the National Counterterrorism Center.
Moreover, the Pentagon announced that Kash Patel, who was the top counter-terrorism adviser on the White House National Security Council, would be Miller's chief of staff.
Patel served as a senior aide to Republican Rep. Devin Nunes, a Trump supporter who headed the House Intelligence Committee.
While working with Nunes, Patel helped release a warrant accusing the FBI and Justice Department of bias against Trump.
But further changes in the Pentagon are raising Democrats 'concerns about whether the United States' national security policy may become unstable, with the Republican Trump leaving the White House.