Famously, Trump lobbed a vague but ominous threat of “fire and fury” at North Korea in August 2017, one of many times when he rattled the American saber in Pyongyang’s direction. These threats were more or less in the mainstream of American foreign policy, although he made them more explicit than other presidents, and it’s not clear the U.S. has any particularly attractive military option in North Korea.

Less famous and much stranger was another August 2017 mention of the military. “We have many options for Venezuela,” he said. “And by the way, I am not going to rule out a military option.” This rattled many people. There had been no previous discussion of invading Venezuela, and for good reason: Although Caracas has often directed inflammatory rhetoric at the U.S., its economic and political crisis is a domestic one and poses no real threat to the United States.

Trump quickly dropped any discussion of sending troops to Venezuela, but the abrupt threat would prove to be an augur of the three more recent cases. Each of them seems to have come about without much consultation with advisers, and each has quickly proven to be more complicated than the president must have hoped.

The suggestion of funding the wall via the military apparently grew out of Trump’s anger at the omnibus spending bill, which did not fund the wall as he hoped. That bill did, however, increase military spending, which Trump celebrated and offered as a rationale for not vetoing the bill. Within days, he began his strange campaign to fund the wall through the Pentagon budget. As my colleague Priscilla Alvarez reported, it doesn’t really work that way. The defense budget is allocated to specific projects, rather than existing as a massive slush fund that the executive branch can direct as it sees fit, meaning that funding the wall would likely require congressional involvement. Of course, if Congress wanted to fund the wall, it would have done so in the first place.

Hence the next idea: send the military to guard the border until the wall is built. Or something.

“We are going to be doing some things—I’ve been speaking with General Mattis—we’re going to be doing things militarily,” he said, referring to the defense secretary. “Until we can have a wall and proper security, we’re going to be guarding our border with the military. That’s a big step. We really haven’t done that before—certainly not very much before.”

Insofar as this has not been done, that’s because it may be illegal; insofar as it is legal, it has already largely been done. Initially, this appeared to mean the U.S. Army, but while the armed forces can assist in law enforcement, it’s not clear that a more or less permanent deployment to guard the border would be legal. What would be legal would be deploying the National Guard—and in fact Presidents George W. Bush and Obama did that on the border. Secretary of Homeland Security Kirstjen Nielsen on Wednesday indicated that’s what Trump intended to do. Such an action will require cooperation with state governors, who command and control the guard, and the troops can’t make arrests, act as police, or use force. In other words, it’s not the simple, unencumbered maneuver Trump intended.