Did you hear the one about a top Trump administration official praising Representative Alexandria Ocasio-Cortez, the liberal firebrand from the Bronx?

You may be waiting for a punch line. But this is not a joke.

Lawrence Kudlow, director of President Trump’s National Economic Council, singled out Ms. Ocasio-Cortez for praise recently — an unusual and illuminating example of people on the right and the left ganging up on an established tenet of the mainstream middle.

What led to this meeting of the minds is a concept called the “Phillips curve.” The economist George Akerlof, a Nobel laureate and the husband of the former Federal Reserve chair Janet Yellen, once called the Phillips curve “probably the single most important macroeconomic relationship.” So it is worth recalling what the Phillips curve is, why it plays a central role in mainstream economics and why it has so many critics.

The story begins in 1958, when the economist A. W. Phillips published an article reporting an inverse relationship between unemployment and inflation in Britain. He reasoned that when unemployment is high, workers are easy to find, so employers hardly raise wages, if they do so at all.