The makeup of President Donald Trump‘s Pentagon leaders has shifted dramatically in the days following the firing of Defense Secretary Mark Esper.

Trump fired Esper on Monday over Twitter, replacing him with acting Defense Secretary Christopher Miller.

On Tuesday, three top senior officials, as well as Esper’s chief of staff, left their roles. The large shifts were alarming to many, as it could be perceived by U.S. adversaries as instability in the defense structure amid the presidential transition.

The chairman of the House Armed Services Committee Adam Smith (D-Washington) said the turnover rate is “dangerous.”

“It is hard to overstate just how dangerous high-level turnover at the Department of Defense is during a period of presidential transition,” Smith said in a statement. “The top policy professional in the department resigning the day after the Secretary of Defense was fired could mark the beginning of a process of gutting the DoD – something that should alarm all Americans.

He continued: “If this is the beginning of a trend – the president either firing or forcing out national security professionals in order to replace them with people perceived as more loyal to him – then the next 70 days will be precarious at best and downright dangerous at worst.”

Those who resigned Tuesday include James Anderson, who held the No. 3 spot in the Pentagon as the acting undersecretary for policy; Joseph Kernan, the undersecretary for Defense intelligence and Esper’s chief of staff, Jen Stewart.

“I want to thank Dr. Anderson, Admiral Kernan and Jen Stewart for their service to the nation and the Department,” Miller said in a statement. “Over their careers each has contributed greatly to the national defense and the future of the Department of Defense. We wish them the best in their next endeavors.”

Andersen was replaced by retired Army general Anthony Tata. Tata had previously faced a heated Senate confirmation hearing over comments he made calling former President Barack Obama a “terrorist leader.” He was subsequently placed in a role that did not mandate a confirmation hearing.