(CNN)Retired Adm. Mike Mullen, a former chairman of the Joint Chiefs of Staff under Presidents George W. Bush and Barack Obama, said Sunday on CNN's "Fareed Zakaria GPS" that he has been "extremely concerned" about military officials like retired Gen. John Kelly acting in political roles in President Donald Trump's administration.
Former Joint Chiefs chairman worries about generals in Trump's White House
Mullen said he worries that having military officials, "without being a politician, without running for office," acting politically could undermine the military as an apolitical institution.
Specifically, he said, he worries a "great deal" about Kelly "indirectly undermining us as a military" because of his role as White House chief of staff, a highly political job.
While many people have told him they have felt comfortable having Secretary of Defense James Mattis, Kelly, and former White House national security adviser H.R. McMaster in Trump's administration, all of whom have been generals, "I don't share that comfort," Mullen said.
Mullen said he's been to countries where the generals and admirals are in charge, which some of the public find comforting, and those are not countries Americans would want to grow up in.
"It's much more a strongman's country than it is a democratic, open, free country," he said.
Mattis, Kelly and McMaster "are not politicians, but they're operating in this political world inside the White House," said Mullen, who served four years under two presidents, adding he understands that world well.
"It is a tough, difficult, political environment," he said, and "it can be very toxic, and it can destroy people."
McMaster was recently ousted as Trump's national security adviser; his last day at the White House was Friday. Meanwhile, CNN has reported on tensions between the President and Kelly, who has become the subject of reports saying his influence in the White House is diminished. Trump on Sunday denied that was the case in a tweet criticizing The Washington Post's reporting on the matter.
Mullen added that he was distressed to see Kelly, a retired four-star general, talk to the press about his experience with the death of his son in Afghanistan as part of an attempt to counter criticisms of Trump's conversation with a widow of a soldier killed in an ISIS ambush in Niger last year.
"To see John Kelly -- and I'll be very specific -- politicize, you know, the death of his son to support the political outcome for the President was very, very distressing to me," Mullen said.
It speaks to the power of that environment, he said, and "the lack of understanding that any of us in the military have about that environment until we get in it and have to operate in it."
"We are apolitical," Mullen said about his fellow military service members. "I get that when we take our uniform off we're citizens," he added, but "he's referred to as General Kelly, not Mr. Kelly, for a reason."