It’s now becoming routine — Trump’s advisers have to walk back his off-the-cuff statements… this time to avert war.

From Jon Chait:

The New York Times has much more detail. Trump improvised his threat without advance consultation with his advisers, none of whom support it. The paper he was holding when he made the statement was about the opioid crisis. Trump “was in a bellicose mood” when he made the statement, due to a Washington Post report that morning about North Korea having miniaturized a nuclear warhead.

Secretary of State Rex Tillerson and Defense Secretary James Mattis have issued more normal-sounding statements intended to supersede the president’s improvised one. (Mattis’s statement redraws the red line, threatening reprisal in return for North Korean actions, rather than threats.) The message of this cleanup is that Trump’s statements do not necessarily represent the position of the U.S. government – a reality most American political elites in both parties already recognize, but which needs to be made clear to other countries that are unaccustomed to treating their head of state like a random Twitter troll.

It is humiliating for the world’s greatest superpower to disregard its president as a weird old man who wanders in front of microphones spouting off unpredictably and without consequence. But at this point, respect for Trump’s capabilities is a horse that’s already fled the barn. New chief of staff John Kelly has supposedly instilled military-style order and message discipline into the administration, but Trump is unteachable. Minimizing the havoc means getting everybody to pretend Trump isn’t really president.

Emphasis mine.