Defense Secretary Pete Hegseth’s inner circle has been engulfed by a contentious leak investigation that Pentagon insiders say led to the dismissal of three senior aides last week, according to five individuals familiar with the matter.

Tensions had been building for weeks between Hegseth’s chief of staff, Joe Kasper, who resigned on Thursday, and the ousted aides: senior advisor Dan Caldwell, deputy chief Darin Selnick, and the chief to the deputy defense secretary, Colin Carroll.

Hegseth's leadership under the microscope

The intense probe into the mishandling of classified information is also raising renewed concerns about Hegseth’s leadership, especially following revelations that he discussed US strike plans on the Yemeni Armed Forces (YAF) within a second Signal chat group that included his wife and other family members.

The leak investigation has had sweeping consequences, sources told The Guardian, prompting Hegseth to significantly shrink his inner circle to just three key figures: acting chief of staff Ricky Buria, formerly his junior military assistant, his attorney Tim Parlatore, and spokesperson Sean Parnell.

At the heart of the probe is the alleged leak of a top-secret document to a journalist, which detailed a range of flexible US military options for retaking the Panama Canal, including deploying troops to the region.

Leak allegedly traced to Dan Caldwell

According to two individuals briefed on the matter, the leak was traced to Dan Caldwell, who reportedly objected to the proposed military strategies tied to Donald Trump’s plans to reclaim the canal.

Caldwell has strongly denied leaking information to a reporter and told Tucker Carlson that he believes the investigation was “weaponized,” especially after facing internal ridicule for supporting military options regarding the Panama Canal.

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Selnick and Carroll, though not primary targets of the leak investigation, were also dismissed and believe they were ousted for challenging Kasper’s leadership, while the Pentagon’s refusal to comment and ongoing internal conflict have left both Pentagon and White House officials unsure who to trust, raising concerns about Hegseth’s inexperience and leadership.

Hegseth's 'charm' good for first six weeks only

According to four Pentagon officials who worked closely with him, Hegseth was seen as relatively successful during his first six weeks in office, displaying charm with world leaders and earning the support of initially skeptical House Freedom Caucus members during budget briefings.

However, the immense responsibility of managing an $800 billion agency with over 2 million service members began to weigh on him, they said, and a string of leaks deepened his suspicion of career staff, despite early hopes that those employees could help him navigate the role effectively.

Caldwell, Selnick vs. Kasper

That strain also impacted his team, which became increasingly divided between those who backed Kasper and dismissed criticism as ambition-fueled, and those aligned with the three ousted aides who viewed Kasper as an ineffective leader.

Kasper reportedly told associates that Caldwell, Selnick, and Carroll were trying to push him out and accused them of stirring up controversy, citing an email from Carroll about potential leaks from the inspector general’s office that he considered unfounded.

He also claimed to have overheard Selnick remark that “the way to get people fired in this place is to get bad headlines on them," according to two officials.

Despite the tensions, senior White House and Pentagon staff increasingly funneled requests through Caldwell and Selnick, who were seen as more efficient, something that reportedly irritated Kasper.

Panama Canal leak prompts probe into nine others

The internal power struggle intensified after the Panama Canal leak, prompting Hegseth to launch an investigation into about nine separate leaks. Kasper, officials said, even suggested involving the FBI and administering polygraph tests to staff.

Caldwell had pushed for the leak investigations to be more narrowly focused, partly because he opposed the idea of the FBI delving into their personal affairs; an attitude that, according to several people he spoke with, may have contributed to the suspicion surrounding him.

Tensions among the ousted aides have lingered. Carroll has reportedly considered filing a defamation lawsuit against Kasper and, shortly after his dismissal, began calling around to ask whether Kasper had ever been seen using cocaine in a previous role.

Kasper, in turn, expressed frustration that some of those calls reached his wife and former clients, telling associates it was absurd to suggest drug use given his security clearance and regular testing.

“It’s so egregiously stupid,” he said when contacted for comment.