Former Secretary of Defense James Mattis recently told The Atlantic that he owed the president and his administration "some silence," explaining that he is keeping his criticisms to himself. The retired Marine Corps general has signaled his displeasure with President Donald Trump's policies in his resignation letter and a carefully-worded essay, but he has avoided directly attacking the president.

"There is a period in which I owe my silence. It's not eternal. It's not going to be forever," he explained, suggesting he may one day share his views on Trump directly.

Visit Business Insider's home page for more stories.

Former Secretary of Defense James Mattis signaled his displeasure with Donald Trump's presidency in his resignation letter and a carefully-worded essay, but he has avoided directly attacking the commander-in-chief. He says he's keeping his criticisms to himself for now, but he won't stay silent forever.

"You don't endanger the country by attacking the elected commander in chief," Mattis told Jeffrey Goldberg, the editor in chief at The Atlantic. "I may not like a commander in chief one fricking bit, but our system puts the commander in chief there," the retired Marine Corps general explained, saying that there is no need for him to criticize Trump and "further weaken him when we're up against real threats."

The US faces challenges from powerful rivals like China and Russia, rogue regimes such as North Korea and Iran, violent extremism, as well as crises as home.

Read more: Defense Secretary James Mattis quits, says his views aren't 'aligned' with Trump as the president upends major US policies

Mattis insists he "had no choice but to leave" the Pentagon, resigning as secretary of defense in December and stepped down at the start of the year over a dispute with the president over Syria, specifically America's role in the ongoing fight against the Islamic State. "You're going to have to get the next secretary of defense to lose to ISIS. I'm not going to do it," he reportedly told the president, who was talking about prematurely pulling all US troops out of Syria.

In his resignation letter, Mattis told Trump he should select a secretary of defense "whose views are better aligned" with his own.

"When you leave an administration over clear policy differences, you need to give the people who are still there as much opportunity as possible to defend the country," Mattis told The Atlantic. "We have to give the people who are protecting us some time to carry out their duties without me adding my criticism to the cacophony that is right now so poisonous."

Read more: Mattis rebukes Trump's leadership in a not-so-subtle op-ed warning against abandoning America's allies

In an essay adapted from his upcoming book, "Call Sign Chaos: Learning to Lead," Mattis condemned leadership that encourages the public mockery and berating of critics, the abandonment of allies, and divisiveness. Many viewed the op-ed published in the Wall Street Journal as a subtle jab at Trump.

In the piece, he explains why he left the Department of Defense, saying, "When my concrete solutions and strategic advice, especially keeping faith with our allies, no longer resonated, it was time to resign, despite the limitless joy I felt serving alongside our troops in defense of our Constitution."

While Mattis' resignation letter and essay appear to be clear rebukes of Trump's policies, the former secretary of defense has yet to go into detail about his tenure as the head of the defense department or offer specific criticisms of the president.

"There is a period in which I owe my silence. It's not eternal. It's not going to be forever," he told Goldberg. Mattis has a story to tell. Apparently, it is only a matter of time until he tells it.