President Barack Obama, right, with Defense Secretary Ash Carter, center, and Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford, stand at attention as the national anthem is played during a memorial ceremony at the Pentagon in Washington, Sunday, Sept. 11, 2016, to commemorate the 15th anniversary of the 9/11 terrorist attacks.
(AP Photo/Manuel Balce Ceneta)
AP Photo/Manuel Balce Ceneta
A mourner holds a photo of her loved one during the 15th anniversary of the attacks of the World Trade Center at the National September 11 Memorial, Sunday, Sept. 11, 2016, in New York.
(AP Photo/Mary Altaffer)
AP Photo/Mary Altaffer
A mourner holds a photo of her loved one during the 15th anniversary of the attacks of the World Trade Center at the National September 11 Memorial, Sunday, Sept. 11, 2016, in New York.
(AP Photo/Mary Altaffer)
AP Photo/Mary Altaffer
A couple kisses while visiting the Pentagon Memorial prior to a Sept. 11 observance ceremony at the Pentagon, Sunday, Sept. 11, 2016.
(AP Photo/Cliff Owen)
AP Photo/Cliff Owen
Candles in memory of the passengers and crew of Flight 93, are carried to the Wall of Names at the Flight 93 National Memorial in Shanksville, Pa, Saturday, Sept. 10, 2016, as the nation marks the 15th anniversary of the Sept. 11 attacks.
(AP Photo/Jared Wickerham)
AP Photo/Jared Wickerham
Visitors make their way through the Flight 93 National Memorial before lit candles are carried to the Wall of Names in memory of the passengers and crew of Flight 93, at the Flight 93 National Memorial in Shanksville, Pa., Saturday, Sept. 10, 2016, as the nation marks the 15th anniversary of the Sept. 11 attacks.
(AP Photo/Jared Wickerham)
AP Photo/Jared Wickerham
A member of the military holds a giant American flat during the national anthem before the first half of an NFL football game between the Atlanta Falcons and the Tampa Bay Buccaneers, Sunday, Sept. 11, 2016, in Atlanta.
(AP Photo/David Goldman)
AP Photo/David Goldman
A mourner holds a photo of their loved one during the 15th anniversary of the attacks of the World Trade Center at the National September 11 Memorial, Sunday, Sept. 11, 2016, in New York.
(AP Photo/Mary Altaffer)
AP Photo/Mary Altaffer
Police officer Eloy Suarez holds an American flag with the names of the people who died during the attacks on the World Trade Center during 15th anniversary ceremony as he stands in the outskirts of the Sept. 11 memorial, Sunday, Sept. 11, 2016, in New York.
(AP Photo/Mary Altaffer)
AP Photo/Mary Altaffer
Mourners observe a moment of silence during the 15th anniversary ceremony of the attacks of the World Trade Center at the National September 11 Memorial, Sunday, Sept. 11, 2016, in New York.
(AP Photo/Mary Altaffer)
AP Photo/Mary Altaffer
An FDNY firefighter walks among flags at the FDNY Memorial Wall on Sunday, Sept. 11, 2016, on the 15th anniversary of the attacks on the World Trade Center in New York.
(AP Photo/Craig Ruttle)
AP Photo/Craig Ruttle
Mourners hold photos of their loved ones during the 15th anniversary of the attacks of the World Trade Center at the National September 11 Memorial, Sunday, Sept. 11, 2016, in New York.
(AP Photo/Mary Altaffer)
AP Photo/Mary Altaffer
A visitor pays tribute to the passengers and crew of Flight 93 at the Flight 93 National Memorial in Shanksville, Pa, Sunday, Sept. 11, 2016, as the nation marks the 15th anniversary of the Sept. 11 attacks.
(AP Photo/Jared Wickerham)
AP Photo/Jared Wickerham
Democratic presidential candidate Hillary Clinton, center, accompanied by Sen. Chuck Schumer, D-N.Y., center left, Rep. Joseph Crowley, D-N.Y., second from left, and New York Mayor Bill de Blasio, center top, attends a ceremony at the Sept. 11 memorial, in New York, Sunday, Sept. 11, 2016.
(AP Photo/Andrew Harnik)
AP Photo/Andrew Harnik
Republican presidential candidate Donald Trump, left, speaks with New Jersey Gov. Chris Christie, right, as he attends a ceremony at the Sept. 11 memorial, in New York, Sunday, Sept. 11, 2016, on the 15th anniversary of the Sept. 11 attacks.
(AP Photo/Andrew Harnik)
AP Photo/Andrew Harnik
Tampa Bay Buccaneers defensive tackle Gerald McCoy warms up with a 9/11 remembrance shirt on before the first half of an NFL football game between the Atlanta Falcons and the Tampa Bay Buccaneers, Sunday, Sept. 11, 2016, in Atlanta.
(AP Photo/David Goldman)
AP Photo/David Goldman
Atlanta Falcons wide receiver Julio Jones warms up wearing cleats in remembrance of 9/11 before the first half of an NFL football game, Sunday, Sept. 11, 2016, in Atlanta.
(AP Photo/David Goldman)
AP Photo/David Goldman
The American flag is seen at the National Harbor, where the 9/11 Memorial Stair Climb event took place Saturday, Sept. 10, 2016.
(WTOP/Kathy Stewart)
