Good morning, Washington. We’re on the brink of the symbolic end of summer. Labor Day traditionally signals the conclusion of our dog days, the retiring of certain white attire, and the ushering in of cooler weather. But, of course, Labor Day is much more than a seasonal marker or a fashion barometer; in a year when public sector unions and their opponents were often in the spotlight, this weekend could be a good time to brush up on your holiday history.