The movement to raise the federal minimum wage has become ever more ambitious. In 2013 proponents deemed $9 an hour acceptable; today the demand is for $15.

Economists point to a crucial question: Will a higher minimum wage reduce the number of jobs for the country’s least skilled workers? President Obama says “there is no solid evidence that a higher minimum wage costs jobs.” On the contrary, a full and fair reading of the evidence shows the opposite. Raising the minimum wage will cost jobs, particularly those held by the...