Edwin Morales holds a framed tribute to 911 victim Ruben Correra on the 18th anniversary of the September 11, 2001 attacks in lower Manhattan in New York, U.S., September 11, 2019.

New York City Fire Department (FDNY) firefighters pause in silence outside Firehouse Engine 10 Ladder company 10 on the 18th anniversary of the September 11, 2001 attacks in lower Manhattan in New York, U.S., September 11, 2019.

Former U.S. President George W. Bush places a wreath as former U.S. Defense Secretary Donald Rumsfeld looks on during the 18th anniversary of September 11 attacks at the Pentagon in Arlington, Virginia, U.S., September 11, 2019.

Flowers are laid on a bench before the 18th annual September 11 observance ceremony at the Pentagon in Arlington, Virginia, U.S., September 11, 2019.

A man pauses near the World Trade Center site on the 18th anniversary of the September 11, 2001 attacks in lower Manhattan in New York, U.S., September 11, 2019.

Officers cary an American flag into ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

U.S. President Donald Trump greets guests and members of the military following a ceremony marking the 18th anniversary of September 11 attacks at the Pentagon in Arlington, Virginia, U.S., September 11, 2019.

A man pauses during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

Airline employees visit the north reflecting pool during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

Flowers are seen left on a fence near the One World Trade Center tower on the 18th anniversary of the September 11, 2001 attacks in lower Manhattan in New York, U.S., September 11, 2019.

Officers ring a bell during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

A boy holds up a photo of a 911 victim during the reading of victims' names during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

U.S. President Donald Trump and first lady Melania Trump place a wreath at the Pentagon Memorial as U.S. Defense Secretary Mark Esper looks on during a ceremony marking the 18th anniversary of September 11 attacks at the Pentagon in Arlington, Virginia, U.S., September 11, 2019.

A woman pauses at the south reflecting pool during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

Connie Dray holds a tribute to her cousin and 911 victim Mary Lou Hague on the 18th anniversary of the September 11, 2001 attacks in lower Manhattan in New York, U.S., September 11, 2019.

The U.S. flag flies at half staff at the U.S. Capitol to mark the 18th anniversary of September 11 attacks in Washington, U.S., September 11, 2019. Image used for illustrative purpose

U.S. President Donald Trump and first lady Melania Trump observe a moment of silence to mark the 18th anniversary of September 11 attacks on the South Lawn of the White House in Washington, U.S., September 11, 2019. Image used for illustrative purpose

Mennonite singers perform in lower Manhattan near the World Trade Center site on the 18th anniversary of the September 11, 2001 attacks in lower Manhattan in New York, U.S., September 11, 2019.

Boys stand at the edge of the south reflecting pool during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

An American flag is seen left in the egraved names of 911 victims at the edge of the north reflecting pool during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

Mourners of 911 victims place flowers at the edge of the north reflecting pool during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

A woman stands with flowers and a photograph during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

A man wipes away tears during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

A man hugs a woman during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

Nick Haros from Ocean County, New Jersey, who lost his mother Francis Haros in World Trade Center, reading 911 victims' names makes comments referencing U.S. Rep. Ilhan Omar (D-MN) during ceremonies commemorating the 18th anniversary of the September 11, 2001 attacks at the 911 Memorial in lower Manhattan in New York, U.S., September 11, 2019.

Josephine Strenta from New Jersey, pauses in silence as she stands near the World Trade Center site on the 18th anniversary of the September 11, 2001 attacks in lower Manhattan in New York, U.S., September 11, 2019.

Albert Liguori, 50 from Staten Island, photographs under the Tribute in Light, lit to commemorate the 18th anniversary of September 11, 2001 attacks in New York City, U.S., September 10, 2019.

Military personnel gather before the 18th annual September 11 observance ceremony at the Pentagon in Arlington, Virginia, U.S., September 11, 2019.

New York City Fire Department (FDNY) firefighters stand at attention outside Firehouse Engine company 10 Ladder company 10 near the World Trade Center site on the 18th anniversary of the September 11, 2001 attacks in lower Manhattan in New York, U.S., September 11, 2019.