For much of the past few generations, the debate over balancing the federal budget has been a central feature of every presidential campaign. But over time, the goalposts have moved. As the amount of red ink has grown steadily larger, the suggested time frames to restore balance have gotten increasingly longer, while the suggested cuts in government spending have gotten increasingly shallower. In recent years, talk of balancing the budget gave way to vague promises such as “cutting the deficit in half in five years.” In the current campaign, however, it appears as if the goalposts have been moved so...