The concept was widely discussed again in 2009 and subsequent years in the context of the Obama administration’s stimulus package, which aimed to jolt the United States out of the deep recession. A Nexis search shows the phrase “pump priming” or its variants appeared in 1,073 news articles in major publications in 2009 alone, and they are almost all referring to economics, not water pumps.

In fact, arguably “priming the pump” is now a “dead metaphor,” or a metaphor in which the original evocative meaning is largely lost. Not many people have a home water pump they need to prime anymore, after all. Other dead metaphors include “champing at the bit” (technically a reference to obstreperous horses) or “selling like hot cakes” (an early term for pancakes, which were in high demand in the 19th century).

Does Trump really think that he invented it?

A more generous reading of the interview with The Economist suggests that perhaps he didn’t literally mean that he came up with the term on his own; he seemed to know that it was a phrase that the editors might have already heard. Still, this fits with a pattern in which the president seems to learn of widely known, widely discussed concepts and view them as novel and revelatory.

For example, he seemed surprised when the Chinese president explained why his country couldn’t simply coerce North Korea into more agreeable behavior, and he has expressed wonderment that health care policy is complicated.

Is now a really good time to be priming the pump?

In Keynesian economic theory, the strategy makes the most sense when there are underutilized economic resources to be tapped, such as during a recession or depression. While the United States economy probably isn’t yet at full capacity, with the unemployment rate at 4.4 percent it does seem to be closing in on full employment. Factories are running closer to full speed, among other evidence that the economy is hardly depressed.