President Donald Trump has had few tranquil periods during his six months in office, and so far as we can tell he prefers cacophony over calm.

How else to explain his announcement Wednesday — by way of Twitter, of course — that “the United States Government will not accept or allow Transgender individuals to serve in any capacity in the U.S. Military.”

In a more conventional presidency we’d be inclined to brand such an impromptu decision as a diversion, a classic political ploy.

But the reality is that Trump’s rejection of transgender members of the military creates not only a distraction from his other difficulties but rather opens an entirely new chapter on capricious decisions.

Following the surprise announcement of the ban, Marine Corps Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, wrote in a memo to other military leaders:

“I know there are questions about yesterday’s announcement on the transgender policy by the president. There will be no modifications to the current policy until the president’s direction has been received by the secretary of defense and the secretary has issued implementation guidance.”

White House press secretary Sarah Huckabee Sanders said Wednesday, “Implementation is something that the Department of Defense and the White House have to work together to lawfully determine.”

It would seem that if the president was truly concerned about distracting the military from its mission, he’d have consulted with his Joint Chiefs of Staff about the ban before sending out the inflammatory tweet.

Nor is that the only troubling aspect of the president’s timing.

Just a day before Mr. Trump’s tweet, The Washington Post, citing a Defense Intelligence Agency estimate, reported that North Korea, by sometime in 2018, might be able to build a missile that could deliver nuclear warheads to North America.

President Trump has vastly more important military matters to deal with. And he should make those decisions after consulting with his military advisers.