“Here’s how the American History Museum, the National Postal Museum and more are reflecting on the tragedy…reminders of September 11, 2001, are scattered throughout the Smithsonian Institution’s collections. A warped piece of steel taken from Ground Zero. A damaged mail collection box that once stood across the street from World Trade Center Building 5. An Airfone recovered from the wreckage of United Airlines Flight 93. A clock frozen at the moment an airplane crashed into the Pentagon, knocking the object off the wall. Tangible traces of an American tragedy, these artifacts and others will feature heavily in the Smithsonian’s upcoming commemoration of 9/11. “After two decades, we continue to feel the lasting and complex personal, national and global ramifications of the terrorist attacks of Sept. 11, 2001,” says Anthea M. Hartig, director of the National Museum of American History (NMAH), in a statement. “At the [museum], we commit to keeping the memory of that day alive by working with a wide range of communities to actively expand the stories of Americans in a post-September 11 world.”…