President Donald Trump and first lady Melania Trump participate in a moment of silence honoring the victims of the Sept. 11 terrorist attacks, on the South Lawn of the White House, Wednesday, Sept. 11, 2019, in Washington. (Evan Vucci/AP)
Flowers rest on a bench bearing a name in memory of retired U.S. Army Lt. Col. Gary Smith before a ceremony in observance of the 18th anniversary of the Sept. 11 attacks at the Pentagon in Washington, Wednesday, Sept. 11, 2019. (Patrick Semansky/AP)
President Donald Trump and first lady Melania Trump place a wreath and will participate in a moment of silence honoring the victims of the Sept. 11 terrorist attacks, Wednesday, Sept. 11, 2019, at the Pentagon. (Evan Vucci/AP)
A U.S. flag hanging from a steel girder, damaged in the Sept. 11, 2001, attacks on the World Trade Center, blows in the breeze at a memorial in Jersey City, N.J., Sept. 11, 2019, as the sun rises behind One World Trade Center building and the re-developed area where the Twin Towers of World Trade Center once stood in New York City on the 18th anniversary of the attacks. (J. David Ake/AP)
New York City firefighters take a position in front of a memorial on the side of a firehouse adjacent to One World Trade Center and the 9/11 Memorial site during ceremonies commemorating the 18th anniversary of the 9/11 terrorist attacks in New York on Wednesday, Sept. 11, 2019. (Craig Ruttle/AP)
A man holds a photo of a victim during a ceremony marking the 18th anniversary of the attacks of Sept. 11, 2001, at the National September 11 Memorial, Wednesday, Sept. 11, 2019, in New York. (Mark Lennihan/AP)
People walk past an American flag at the start of a work day, at the Oculus, part of the World Trade Center transportation hub in New York, Wednesday, Sept. 11, 2019, on the 18th anniversary of 9/11 terrorist attacks. (Wong Maye-E/AP)
A photograph of fallen firefighter Leon Smith, Jr. is held up during a ceremony marking the 18th anniversary of the attacks of Sept. 11, 2001 at the National September 11 Memorial, Wednesday, Sept. 11, 2019 in New York. (Mark Lennihan/AP)
The names are read of victims of the Sept. 11 attacks during a ceremony marking the 18th anniversary at the National September 11 Memorial, Wednesday, Sept. 11, 2019 in New York. (Mark Lennihan/AP)
A woman pays respects at the Wall of Names at the Flight 93 National Memorial in Shanksville, Pa. after a Service of Remembrance Wednesday, Sept. 11, 2019, as the nation marks the 18th anniversary of the Sept. 11, 2001, attacks. The Wall of Names honor the 40 people killed in the crash of Flight 93. (Gene J. Puskar/AP)
