This picture taken 26 December 2011 shows the Pentagon building in Washington, DC.  The Pentagon, which is the headquarters of the United States Department of Defense (DOD), is the world's largest office building by floor area, with about 6,500,000 sq ft (600,000 m2), of which 3,700,000 sq ft (340,000 m2) are used as offices.  Approximately 23,000 military and civilian employees and about 3,000 non-defense support personnel work in the Pentagon. (Photo credit should read STAFF/AFP via Getty Images)
Starr: White House is cleaning house for political reasons
01:39 - Source: CNN
CNN  — 

The deputy chief of staff to the secretary of defense has resigned, a US defense official told CNN on Thursday, becoming the latest official to depart the Pentagon amid a purge that began Monday when President Donald Trump fired Defense Secretary Mark Esper.

Alexis Ross has resigned, the official said, joining now-former chief of staff Jen Stewart and the top Pentagon officials overseeing policy and intelligence, all three of whom had submitted their resignations Tuesday.

The flurry of changes within the department in recent days has put officials inside the Pentagon on edge and fueled a growing sense of alarm among military and civilian officials, who are concerned about what could come next. The moves will likely only add to the sense of chaos within the Pentagon following Trump’s firing of Esper by tweet.

Stewart was replaced by Kash Patel, who most recently served as senior director for counterterrorism at the White House National Security Council and is seen as much more ideological and closely linked to Trump.

Esper was replaced by Christopher Miller, who was the director of the National Counterterrorism Center. The President jettisoned him two days after his Democratic opponent, Joe Biden, was projected as the winner of the presidential election, a conclusion that Trump has refused to publicly acknowledge.

Sources told CNN’s Jake Tapper Tuesday that the White House now seems focused on going after Esper’s under secretaries at the Defense Department in the wake of his firing on Monday. The sources said the effort may be because Esper and his team were pushing back on a premature withdrawal from Afghanistan that would be carried out before the required conditions on the ground were met, and other pending security issues.

While top officials have been dealing with Trump’s unpredictable decision making since he took office, the current level of uncertainty has risen steadily since the election. Concerns are growing that a chaotic transition period could undermine national security.

Among those who also assumed new roles at the Department of Defense this week are controversial retired Brig. Gen. Anthony Tata, who moved into the Pentagon’s top policy role, taking over the duties of James Anderson, who resigned Tuesday.

Tata had been nominated to be under secretary of defense for policy this summer but his nomination was withdrawn because of bipartisan opposition.

Retired Navy Vice Adm. Joseph Kernan, the under secretary of defense for intelligence, also left his position, according to another defense official. It was not immediately clear if Kernan had resigned or was fired, but his departure has been accelerated.

This story has been updated with additional reporting.

CNN’s Caroline Kelly, Barbara Starr and Zachary Cohen contributed to this report.