After days of fiery talk of possible military intervention in the North Korea nuclear stand-off, Pentagon officials late last week suddenly found themselves digesting a surprising piece of breaking news.

President Donald Trump, in the middle of a working vacation, stood before cameras and said the United States was also mulling options against crisis-hit Venezuela, "including a possible military option if necessary."

The announcement, seemingly out of left-field, sent Pentagon staff scrambling. 

They eventually noted that the military plans for any number of situations, and that its Southern Command had not received any Venezuela orders.

The surreal situation was just the latest step along an increasingly well-trodden path, where the military finds itself caught off-guard by its commander-in-chief.

Such was the case again this week, after Trump said left-wing counter-protesters were partly responsible for deadly violence at a white supremacist rally in Virginia and claimed there were "very fine people on both sides."

While not addressing his comments directly, top military leaders issued statements denouncing racism and intolerance.

The move was seen as a radical departure for the Pentagon, which considers itself impartial and ordinarily steers clear of the political arena.

- Fire and fury -

Trump dominated global headlines when he promised "fire and fury like the world has never seen" if Kim Jong-Un continued to threaten America with his growing ballistic missile capabilities and later underscored the message by saying military options were "locked and loaded."

How carefully Trump had calibrated his message with the Pentagon is unknown. 

Pentagon spokesman Colonel Rob Manning said only that Defense Secretary Jim Mattis is in "close and constant contact with the president."

Mattis and Secretary of State Rex Tillerson later penned an opinion piece that helped cool the rhetoric, saying America has "no interest" in regime change in Pyongyang and stressing diplomatic solutions.

Trump blindsided the military again last month, when he tweeted he was scrapping an Obama-era policy of more than a year allowing transgender troops to serve openly.

Trump's announcement came while Mattis was on vacation, and officials couldn't even say for sure if he knew ahead of time that Trump wanted to reinstate the ban.

Since the July 26 tweets, several senior military officials have voiced unease over the policy shift, with the head of the Coast Guard saying he would not "break faith" with transgender personnel.

Such spontaneous announcements create a particularly delicate position for Mattis, who does not want to contradict his boss but must reassure those unnerved by Trump's messages.

"It puts military leaders in the hard position of speaking out against the commander-in-chief," noted Lauren Fish, a research associate at the Center for a New American Security think tank. 

"They are trying to hold the line (when) they don't see policies that are fully vetted and filled out."

For now at least, the existing transgender policy remains in place.

- Crazy like a fox? -

Trump's willingness to circumvent White House and Pentagon messaging norms has baffled some observers.

The Pentagon and the president's National Security Council ordinarily coordinate closely on policy announcements -- and certainly around talk of military action.

John Hannah, senior counselor at the Foundation for Defense of Democracies who worked under three previous administrations, including as former vice president Dick Cheney's national security advisor, said it is unclear whether Trump's national security pronouncements are part of a well-considered strategy, or are "rhetorical eruptions of an undisciplined mind and foreign policy neophyte."

"Is he crazy, or crazy like a fox?" Hannah said. 

"Those willing to give the president the benefit of the doubt are more likely to believe that there's method to the madness. They see him more often than not playing a more sophisticated –- albeit high-risk –- game of good cop, bad cop."

He told AFP the jury is still out on whether Trump is creating messes that Mattis and Tillerson are constantly cleaning up, or whether over-the-top statements and unpredictability actually create leverage to pressure adversaries and allies.

For Fish, of the Center for a New American Security, part of the issue is that Trump is still unaccustomed to how government works.

"What is new to him is the Pentagon isn't a family business where just a quick tweet or quick comment can change the whole ship," Fish said. 

She told AFP that the lack of coordination around Trump's announcements could affect civil-military relations because his messages distract Pentagon planners from the most important tasks at hand. 

"They are chasing rabbits that are running around, rather than thinking about where does the US want to be in two years, what does the operating environment look like and how do we use all of the levers of national power to get the effects we want," she said.

Retired admiral Mike Mullen, who was formerly chairman of the Joint Chiefs of Staff, warned of real-world consequences to impromptu messages, saying Trump's North Korea rhetoric risked constraining the military.

"It eliminates maneuver space for him because it looks like brinkmanship to me," Mullen told NBC News