Donald Trump has an unfortunate habit of describing phone calls that happened only in his imagination, though he presents them to the public as if they were real.

In August, for example, the president described a phone conversation with Mexican President Enrique Pena Nieto that, in reality, never occurred. Before that, Trump was excited about a phone call he’d received from the head of the Boy Scouts, which also hadn’t happened. In July, he offered details of a phone conversation with the head of a large nation, with over 300 million people, who complained to the American president about the foreign country’s 9% GDP growth rate.

There is no such country. Though Trump talked about the phone call more than once, he apparently made it up.

With this in mind, it seemed quite important over the weekend when the American president told reporters, practically as an aside, that North Korean officials recently called U.S. officials to discuss diplomatic engagement. “Now we’re talking,” Trump said, referring to North Korea. “They, by the way, called up a couple of days ago; they said, ‘We would like to talk.’ And I said, ‘So would we, but you have to de-nuke.’”

And while that seemed like an important breakthrough, it now appears the conversation Trump described never occurred.

The White House said Monday that Donald Trump had been referring to a call with South Korea’s leader when he appeared to suggest a landmark direct contact with the nuclear North. […] A senior administration official, speaking on condition of anonymity, told AFP that Trump had in fact been referencing a call he had on Thursday with South Korean President Moon Jae-in.

At the risk of sounding picky, there’s a big difference between the two countries. One is an ally, one isn’t. A phone call from one is routine; a phone call from the other is important.

This isn’t the kind of mistake an American president should make casually when describing a tense national security situation.

And more to the point, why is it, exactly, that Trump keeps telling people about phone calls that never happened? The next time he describes the details of some important conversation he claims to have had, why in the world would anyone believe him?