A prominent retired four-star admiral says that several former generals have left President Donald Trump’s administration because their advice and many years of military experience did not make a difference in swaying the White House on key national security issues.

Former NATO Supreme Allied Commander Adm. James Stavridis noted in Time Magazine Thursday that former Marine Corps Gen. Jim Mattis, Trump’s former defense secretary, is only the latest high-profile departure. That list now includes his former chief of staff, retired Marine Corps Gen. John Kelly, and his former national security adviser, retired Army Lt. Gen. H.R. McMaster.

“The President famously does not actually read the voluminous policy papers with which he is presented. From the perspective of a senior military mind, this would be akin to a car refusing to be gassed up,” Stavridis wrote.

“In the end, each of them had to ask himself, At what point does my serving in this White House become less a guardrail and more an enabler? And what will it ultimately mean that the hard-won credibility of my life and career supported the work of this administration,” Stavridis wrote.

Trump made no secret of his skepticism of military leadership even before he took office, telling voters in 2015 “I know more about ISIS than the generals do. Believe me.”

In the time that’s followed, Trump has lashed out at some of the most revered military generals of the most recent generation.

In November he called retired Navy Adm. Bill McRaven, a career SEAL who led the raid against Osama bin Laden a “Hillary Clinton fan” and chided McRaven for not getting bin Laden “sooner.”

In January, Trump questioned even the value of retired Army Gen. Stanley McCrystal’s four-star rank, putting “general” in quotation marks in a debasing tweet.

Last, on Wednesday, after much backlash on the departure of Mattis, Trump said during a cabinet meeting that his former defense secretary didn’t actually resign, but was fired, despite Mattis releasing a much-publicized letter announcing his policy splits with the White House.

Trump also questioned Mattis' accomplishments.

“What’s he done for me?” Trump said Wednesday to reporters during a White House cabinet meeting. “How has he done in Afghanistan? Not too good. Not too good. I’m not happy with what he’s done in Afghanistan. And I shouldn’t be happy.”

“I mean, I wish him well. I hope he does well,” Trump said. “But as you know, President Obama fired him, and essentially so did I. I want results.”

“I think I would’ve been a good general, but who knows,” Trump said.