The presidents stood next to each other, with their wives, listening as the families of the victims read the names of lost loved ones. Above them, a vast American flag billowed from One World Trade Center, the tower that is rising where two fell a decade ago.
It was the first time President Obama and former President George W. Bush had stood together on this hallowed ground. Mr. Bush declined Mr. Obama’s invitation to join him at ground zero last May, days after the raid that killed Osama bin Laden.
But on this bright morning, they stood shoulder to shoulder behind a bulletproof screen — two commanders in chief whose terms in office are bookends for considering how the United States has changed since Sept. 11, 2001, particularly in its response to terrorism.