Defense Secretary Pete Hegseth arrived at the Pentagon in January with almost no government experience and huge ambitions to remake the way the military was being run.

In just three months in office, Mr. Hegseth, a former Fox News host, has instead produced a run of chaos that is unmatched in the recent history of the Defense Department.

Mr. Hegseth’s inner circle of close advisers — military veterans who, like him, had little experience running large, complex organizations — is in a shambles. Three members of the team he brought with him into the Pentagon were accused last week of leaking unauthorized information and escorted from the building.

A fourth recently departed member of Mr. Hegseth’s team, John Ullyot, who had been his top spokesman, accused Mr. Hegseth of disloyalty and incompetence in an opinion essay in Politico on Sunday. “The building is in disarray under Hegseth’s leadership,” Mr. Ullyot wrote.

The discord, according to current and former defense officials, includes: screaming matches in his inner office among aides; a growing distrust of the thousands of military and civilian personnel who staff the building; and bureaucratic logjams that have slowed down progress on some of President Trump’s key priorities, such as an “Iron Dome for America” missile-defense shield. The officials spoke on the condition of anonymity to discuss internal business.

Adding to the dysfunction, Elon Musk’s Department of Government Efficiency has set a loose target of slashing as many as 200,000 jobs from the Pentagon’s civilian work force of 750,000, a level of cuts Mr. Hegseth has warned would cripple some critical functions within the department, three current and former defense officials said.

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