The Democratic Party is in the early stage of a much-needed debate about its economic agenda. But reshaping the future is no reason to rewrite the past. That’s what many self-styled progressives are now doing with their no-holds-barred rejection of Bill Clinton’s economic legacy.

The latest participant in this self-defeating historical amnesia is AFL-CIO President Richard Trumka, who said in a recent interview that the Clinton administration was “the beginning of the schizophrenic days, when they needed workers’ votes but...