Memorials were also held across the globe. Outside Buckingham Palace in London, during the changing of the guard, the guardsmen’s band played “The Star-Spangled Banner,” as it had after Sept. 11, 2001. At the NATO headquarters in Brussels, the secretary-general stood in front of a piece of twisted metal from the World Trade Center for a moment of silence.
Mr. Bush and Vice President Kamala Harris both took part in a ceremony at the Flight 93 National Memorial in Pennsylvania, during which the names of the 40 passengers and crew members on the plane were read aloud.
Ms. Harris said that the Sept. 11 attacks had demonstrated how “fear can be used to sow division.” She stressed that America’s diversity was its greatest asset and encouraged the country to reflect on the sacrifice made by those who died.
“On this 20th anniversary, on this solemn day of remembrance, we must challenge ourselves to, yes, look back,” Ms. Harris said. “For the sake of our children. For the sake of their children. And for that reason, we must also look forward. We must also look toward the future. Because in the end, that is what the 40 were fighting for: their future, and ours.”
Hours later, Mr. Biden and Dr. Biden arrived to lay a wreath at the memorial. Then, holding hands, they strode quietly toward a boulder marking the area where the plane hit the ground and spent time with the families of victims.
The president and the first lady then traveled with Ms. Harris and her husband to another wreath ceremony at the Pentagon in Arlington, Va., where 184 people were killed after a plane hit the building’s west side.
Earlier on Saturday, the Department of Defense unfurled a large American flag on the side of the building and held a memorial ceremony there.
“The hallways that we tread were the ones where so many of them walked,” said the secretary of defense, Lloyd J. Austin III. “It will always be our duty to fulfill their missions and live up to their goodness and to stand guard over this democracy.”
Reporting was contributed by Corey Kilgannon and Andy Newman from New York; Thomas Kaplan and Aishvarya Kavi from Washington; Alan Blinder from Columbus, Ohio; Lauryn Higgins from Lincoln, Neb.; and Robert Chiarito from Chicago.