Simplify the following text for a Grade 8 native English-speaking person.
Original: On September 14 , 2001 , in the aftermath of the September 11 attacks , Graham led a prayer and remembrance service at Washington National Cathedral , which was attended by President George W. Bush and past and present leaders .
Simplified: On September 14 , 2001 , shortly after the September 11 , 2001 attacks , Graham led prayer at the Washington National Cathedral . President George W. Bush went to this service .