NEW YORK (AP) — Three presidents and their wives stood somberly side by side at the National September 11 Memorial, sharing a moment of silence to mark the anniversary of the nation’s worst terror attack with a display of unity. Presidents Joe Biden, Barack Obama and Bill Clinton all gathered at the site where the World Trade Center towers fell two decades ago. They each wore blue ribbons and held their hands over their hearts as a procession marched a flag through the memorial. The display was watched by hundreds of Americans, some carrying photos of loved ones lost in the attacks. The president is spending Saturday paying his respects at the trio of sites where the planes crashed.