SHARPSBURG, MD – SEPTEMBER 15: Reenactors take part in a recreation entitled “Dunker Church” as people gather to mark the 150th anniversary of the Battle of Antietam on Saturday September 15, 2012 just outside of Sharpsburg, MD, not far from the Antietam National Battlefield. The true anniversary of the battle is September 17th. It is known as being the bloodiest battle for a single day in U.S. history. (Photo by Matt McClain for The Washington Post)