Accepting his party’s nomination in 1984, Democrat Walter Mondale vowed to cut the deficit with a memorable line about the tough medicine either he or Ronald Reagan would have to administer to the country. “Let’s tell the truth,” Mondale said, “Mr. Reagan will raise taxes, and so will I. He won’t tell you. I just did.” Now, as Labor Day marks the final stretch of another presidential campaign, it’s time for another round of truth-telling. The best possible outcome in November for the...