Let's say you're preparing dinner and you realize with dismay that you don't have any certified organic Tuscan kale. What to do? Here's how Michelle Obama handled this very predicament Thursday afternoon: The Secret Service and the D.C. police brought in three dozen vehicles and shut down H Street, Vermont Avenue, two lanes of I Street and an entrance to the McPherson Square Metro station. They swept the area, in front of the Department of Veterans Affairs, with bomb-sniffing dogs and installed magnetometers in the middle of the street, put up barricades to keep pedestrians out, and took positions with...