9/11 remembered around U.S.

President Donald Trump and first lady Melania Trump stand for a moment of silence to mark the anniversary of the Sept. 11 terrorist attacks on the South Lawn of the White House on Sept. 11, 2017, in Washington.

A man stands at the edge of a waterfall pool at ground zero during a ceremony on the 16th anniversary of the 9/11 attacks in New York on Sept. 11, 2017.

John Pristas, a firefighter for the Cranberry Township Volunteer Fire Company in Pennsylvania, walks between a granite marker and a piece of structural steel from one of the collapsed New York trade towers on Sept. 11, 2017.

In a Sept. 9, 2017, photo, Kearney firefighter George Wiedel climbs stairs with his son Greyson strapped to his back during a 9/11 Memorial Stair Climb at Werner Park in Papillion, Neb.

President Donald Trump and first lady Melania Trump stand for the national anthem during a ceremony to mark the anniversary of the Sept. 11 terrorist attacks on Sept. 11, 2017, at the Pentagon.

New York Mayor Bill de Blasio attends a ceremony at ground zero in New York on Sept. 11, 2017.

An American flag stands over the names of the victims of the 9/11 terrorist attacks before a ceremony at ground zero in New York on Sept. 11, 2017.

People hold up signs with the names and pictures of victims of the 9/11 terrorist attacks during a ceremony at ground zero in New York on Sept. 11, 2017.

People gather at the side of the north waterfall pool before the ceremony at ground zero in New York on Sept. 11, 2017.

West Virginia National Guard Staff Sgt. Sean Ruth, right, mourns the loss of his father, Army Chief Warrant Officer 4 William Ruth, who died in the Sept. 11 attack on the Pentagon, while at a memorial at the Pentagon on Sept. 11, 2017. He was visiting with his family including his daughter Ayslynn Ruth, 4.

President Donald Trump speaks during a ceremony to mark the anniversary of the Sept. 11 terrorist attacks on Sept. 11, 2017, at the Pentagon.

White House chief economic adviser Gary Cohn, left, White House senior adviser Jared Kushner, center, and Ivanka Trump speak before the beginning of a ceremony to mark the anniversary of the Sept. 11 terrorist attacks on the South Lawn of the White House on Sept. 11, 2017, in Washington.