President Barack Obama and First Lady Michelle Obama, former President George W. Bush and former First Lady Laura Bush at the National September 11 Memorial

President Barack Obama and First Lady Michelle Obama, along with former President George W. Bush and former First Lady Laura Bush, walk along the western edge of the North Pool at the National September 11 Memorial in New York, N.Y., prior to a commemoration ceremony on the tenth anniversary of the 9/11 attacks, Sunday, Sept. 11, 2011.