A favorite "progressive" trope is that America's middle class has stagnated economically since the 1970s. One version of this claim, made by Robert Reich, President Clinton's labor secretary, is typical: "After three decades of flat wages during which almost all the gains of growth have gone to the very top," he wrote in 2010, "the middle class no longer has the buying power to keep the economy going."

This trope is spectacularly wrong.

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