Donald Trump has said many strange things in recent interviews. One can only imagine, for example, what America’s military leaders thought about his rambling, word-salad musings about how to improve our aircraft carriers.

Over here in Econoland, however, the buzz was all about Trump’s expressed willingness, in an interview with the Economist magazine, to pursue tax cuts even if they increase deficits, because “we have to prime the pump” — an expression he claimed to have invented. “I came up with it a couple of days ago and I thought it was good.”

Actually, the expression goes back generations — F.D.R. used it in a 1937 speech — and has been used many times since, including several times by Trump himself. What’s more, it’s a bad metaphor for modern times. Twenty years ago, in a paper warning that Japanese-style problems might eventually come to America, I urged that the phrase be withdrawn from circulation: “Since hardly anybody in the thoroughly urbanized societies of modern America and Japan has any idea what it means to prime a pump, I hereby suggest that we rename this the jump-start strategy.”

But why should anyone besides pedants care?

First, a mind is a terrible thing to lose. Senior moments, when you can’t remember a name or phrase, or misremember where it came from, happen to many of us. But that Economist interview was basically one long senior moment — and it wasn’t very different from other recent interviews with the commander in chief of the world’s most powerful military.