AMNA NAWAZ: There are new questions tonight about what the future of the Pentagon will look like, as another central member of the U.S.

military team steps down.

GEOFF BENNETT: Nick Schifrin looks at how the changes could affect America's war effort and the Pentagon for years to come.

NICK SCHIFRIN: He was the baby-faced modernizer, the 38-year-old veteran and former investment banker who pushed the Army to embrace drones and transform how it buys weapons.

But Army Secretary Dan Driscoll eventually clashed with his boss, Secretary Pete Hegseth, and their boss, the president, declined to stop Hegseth from pushing him out.

His departure creates a leadership void after the forced retirement of the Army's popular top general, Randy George, with no replacement.

DAN DRISCOLL, Former U.S.

Secretary of the Army: I drove straight to General George's house.

We walked right in and we all gave him a hug.

NICK SCHIFRIN: After George's firing in April, Driscoll testified that, at the end of the day, the president and Secretary Hegseth choose their people.

DANIEL DRISCOLL: The civilian leadership, the design of our system is that they get to pick the leaders that they want.

NICK SCHIFRIN: Which is what Hegseth warned before he became secretary.

PETE HEGSETH, U.S.

Defense Secretary: Well, first of all, you got to fire -- you know, you got to fire the chairman of the Joint Chiefs and you got to fire this -- I mean, obviously, you're going to bring in a new secretary of defense, but any general that was involved, general, Admiral, whatever that was involved in any of the DEI woke (EXPLETIVE DELETED) it's got to go.

NICK SCHIFRIN: He's followed through on those threats, not only Chairman of the Joints Chief C.Q.

Brown, who had previously been the first Black military service chief, but also the female military service chiefs, the chief of naval operations, Lisa Franchetti, and Coast Guard Commandant Admiral Linda Fagan, also the Air Force's top General David Allvin, regional four-star commanders, including in Latin America, Admiral Alvin Holsey, in the middle of the U.S.'

largest anti-drug boat strike campaign in history.

Also popular generals, including C.D.

Donahue, described by colleagues as one of his generation's best leaders, as well as multiple top military lawyers known as judge advocate generals.

PETE HEGSETH: If the words I'm speaking today are making your heart sink, then you should do the honorable thing and resign.

NICK SCHIFRIN: It's not only the people.

Hegseth has tried to refashion the military itself in his own image.

PETE HEGSETH: It's completely unacceptable to see fat generals and admirals in the halls of the Pentagon.

NICK SCHIFRIN: And he's launched a campaign of what he's called ending the war on warriors.

PETE HEGSETH: We are leaving wokeness and weakness behind.

No more dudes in dresses.

We're done with that (EXPLETIVE DELETED).

NICK SCHIFRIN: The Pentagon and White House argue Hegseth is delivering on the president's priorities and helping steward the military through multiple conflicts around the world.

Today, Driscoll's departure sparks a mostly partisan response.

Foreign Affairs Committee Chairman Brian Mast: REP.

BRIAN MAST (R-FL): Pete Hegseth is doing a great job making sure that people in the ranks across the board from bottom to top are focused on one thing alone, their capabilities.

NICK SCHIFRIN: Senate Armed Services Committee Ranking Member Democrat Jack Reed.

SEN.

JACK REED (D-RI): Hegseth, as I said from the very beginning, was unqualified to be secretary of defense, both operationally, experientially, and also temperamentally.

J.D.

VANCE, Vice President of the United States: He's a man of integrity.

He's a man of character.

NICK SCHIFRIN: Driscoll is a friend and one-time aide to Vice President Vance, a former Army lieutenant deployed to Iraq and son and grandson of a soldier, none of which was enough to save his job.

For the "PBS News Hour," I'm Nick Schifrin.