The roar begins in the parking lot at the Pentagon. Within minutes, the slow rumble, mostly of Harley-Davidson motorcycles, makes its way onto Memorial Bridge. Thus begins the Rolling Thunder's First Amendment Demonstration Run. Founded in 1987, the organization raises awareness for people listed as prisoners of war or missing in action in all wars going back to World War I. After making its way across the Memorial Bridge, the wave of motorcycles passes the Lincoln Memorial, rolls onto Constitution Avenue, and rumbles past the National Mall to the Capitol. The bikers then make their way to Independence Avenue and drive past the Mall again before completing their run at Potomac Park, where the cavalcade pays tribute to America's fallen soldiers. The event continues with speakers at the Lincoln Memorial, followed by a musical tribute to veterans. The day ends with a Memorial Day concert at the Capitol. The 2019 event will almost certainly be the biggest of them all, in part because it will also be the last. The unique motorcycle ride will finally come to an end. Biker events have a long history in this country. Bike Week in Daytona Beach, Fla., and the Sturgis Motorcycle Rally in Sturgis, S.D., are two of the biggest, drawing anywhere from 500,000 to 700,000 participants. Those events, however, take place over the course of an entire week. Rolling Thunder's Ride for Freedom attracted more than 500,000...