Visitors to the Flight 93 National Memorial in Shanksville, Pa., participate in a memorial service Thursday ahead of the 19th anniversary of the Sept. 11 attacks.

Visitors to the Flight 93 National Memorial in Shanksville, Pa., participate in a brief memorial service on Thursday, Sept. 10, 2020, as the nation prepares to mark the 19th anniversary of the Sept. 11, 2001 attacks. (AP Photo/Gene J. Puskar)